\ 
 
 ersity of Cincinnati 
 
 Bulletin No, X 
 
 Publications of the University of Gncinnati, 
 Series II. Voi,. II. 
 
 The 
 
 Crayfish of Missouri 
 
 By 
 
 Maty Steele* 
 
 The University Bulletins are Issued Quarterly 
 
 Entered at the Post Office at Cincinnati, Ohio, as second-class matter 
 
 UNIVERSITY PRESS 
 
 Cincinnati, Ohio 
 
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University of Cincinnati 
 
 Bulletin Na X. 
 
 Publications of the University of Cincinnati, 
 Sbribs II. Edited by HOWARD AYERS. voi,. II. 
 
 The Crayfish of Missouri 
 
 By MARY STEELE. 
 
 The University Bulletins are Issued Monthly 
 
 Entered at the Postoffice at Cincinnati, Ohio, as second-class matter 
 
 UNIVERSITY PRESS 
 
 CINCINNATI, O. 
 

 CONTENTS. 
 
 
 Group I. 
 
 C. blandingii. 
 C. hayi. 
 
 Group II. 
 
 C. gracilis. 
 
 Group III. 
 
 C. hartonii. 
 C. setosus. 
 C. ayersii. 
 
 Group IV. 
 
 C. harrisonii. 
 
 C. whitmani. 
 
 C. rinmunis. 
 
 C. rusticus. 
 
 C. medins. 
 
 C. virilis. 
 
 General discusion of the species. 
 
 Immature virilis. 
 
 Variations within the species. 
 
 First and second forms of the males. 
 
 Summary. 
 
 Biliography. 
 
 Explanation of the Plates. 
 
 £ 
 
INTRODUCTION. 
 
 The variations found within a species has been a subject 
 of interest among scientists from the earliest history of bio- 
 logical sciences down to the present time. What it takes to 
 constitute a species and at what point differences are impor- 
 tant enough and constant enough to separate individuals in- 
 to different species are still disputed questions. 
 
 In my taxonomic studies upon the crayfish of Missouri, 
 Dr. Ayers called attention to the fact that the species of 
 Cambarus within this state presented favorable material for 
 the study of variations and further that the field was the 
 more attractive because so little work of this kind had been 
 done in the Mississippi River basin. 
 
 I have had an opportunity to examine a large number 
 of individuals belonging to several species and have made a 
 special study of the variations which a species presents. 
 This has led me to conclude that, to say the least, it is 
 very injudicious to name a species without having examined 
 an abundance of material. 
 
 There is too great a tendency to overlook variations 
 within a species and to multiply constantly the number of 
 species much to the confusion of our system of taxonomy. 
 This consideration, together with the fact that little or no 
 work has been done upon the fauna west of the Mississippi 
 by those acquainted with the territory has led me to present 
 this paper for publication. Practically all of the taxonomic 
 work that has been done in thi^ part of the United States 
 has been done by men from the Bast who have made flying 
 trips through the country and collected whatever specimens 
 came in their way. Generally they have not visited the terri- 
 tory but have merely classified material sent them by 
 collectors. 
 
 (5) 
 
Usually the material sent them has been very meagre and 
 the descriptions of habits and habitats has been very 
 inadequate. 
 
 In addition to the work already mentioned, I have also 
 made a long- series of observations upon the first and second 
 forms of the males as found in C. virilis, the results of which 
 are included in this paper. 
 
 During the observations many interesting points were 
 suggested, for which I have as yet been unable to furnish 
 any explanation; but which I hope to be able to further in- 
 vestigate some time in the future. 
 
 I desire to express my indebtedness to Dr. Howard Ayers, 
 for suggesting the general plan of the work and for constant 
 advice and assistance. I am also under obligations to Dr. 
 Chas. Thorn, for material. To Dr. Geo. Lefevre I am in- 
 debted for a careful examination of the MS. 
 
 THE CRAYFISH OF MISSOURI. 
 
 When Dr. Faxon ('85) published his "Revision of The 
 Astacidse, Part I. The Genera Cambarus and Astacus;" there 
 had been reported from Missouri only seven species of cray- 
 fish, all belonging to the genus Cambarus; C. blandingii. 
 Group I; C. diogenes, Group III ; C. medius, C. rusticus, C. 
 immunis, C. harrisonii and C. virilis Group IV. C. bartonii, 
 of Group III, was also included as probably occuring. 
 
 These groups are the subdivisions of the genus Cam- 
 barus, according to Faxon, who has divided the genus into 
 five different groups, basing his division upon the number of 
 hooked thoracic legs and the shape of the first pair of abdom- 
 inal appendages of the male. 
 
 The different species within the groups are distinguish- 
 ed by minor and less constant differences than those which 
 determine the group. Differences in the shape of rostrum, 
 breadth of areola, shape and size of chela, whether spines are 
 few or numerous on carapace and claws, and the general con- 
 tour of body are some of the features that are takeninto con- 
 sideration in determining to what species an individual cray- 
 fish belongs. 
 
 (6) 
 
Since Faxon's paper was published several other species 
 have been identified as native to Missouri. Among- these 
 may be mentioned, C. hayi, Group I; C. gracilis, Group II; 
 C. seiosus, Group III, and C. ayersii, Group III. The last 
 two are blind species. C. ayersii is now described for the 
 first time, and C. setosus, was classified and named by Faxon 
 ('89) and has as yet been reported from no other state. 
 
 Faxon has divided the territory occupied by the different 
 species of Cambarus into two provinces, a southern and a 
 northern one. The southern province embraces the Atlan- 
 tic States south of North Carolina, the Gulf States and Cuba, 
 and is characterized by the prevalence of species belonging 
 to Groups I and II. The northern province includes the 
 Atlantic States north of South Carolina, the Mississippi Val- 
 ley States north of the Gulf States and Canada. In this pro- 
 vince, forms of Group III and IV are dominant. However, 
 species of Groups I and II are found in this province, and 
 likewise species of Groups III and IV are found in the 
 southern province. In fact there are five species from Group 
 III, C. acuminatus, C. latimus, C. extranus, C. girardianus 
 and C. jordani, and also three species from Group IV, C. ala- 
 bamensis, C. comfressus and C. sfinosus that Faxon considers 
 as restricted to the southern province. Only two species 
 of Group I, C. blandingii and C. jyellncidus and two species 
 of Group II, C. simulans and C. gracilis had been reported 
 from the northern province when Faxon published his paper. 
 However, within the last three or four years there has been 
 collected within this state another member of Group I, C. 
 hayi and also a member of Group II, C. gracilis. 
 
 Heretofore C. hayi had been reported from but one state? 
 Mississippi. Doutless other species seemingly restricted to 
 the southern province would also be found in the northern 
 if the territory were carefully searched; but the species 
 which are found in Missouri centainly bear witness to Fax- 
 on's statement that Groups III and IV dominate in the north- 
 ern province; for of twelve species that have been identified 
 as certainly native of Missouri six species belong to Group 
 IV and three to Group III, leaving but three species as mem- 
 bers of Groups I and II. 
 
 (7) 
 
GROUP I. 
 
 Beginning with the members of Group I, I shall give a 
 somewhat detailed account of the species of Cambarus 
 found in Missouri, without going into a systematic des- 
 cription of any except new species. So far only two mem- 
 bers of Group I have been found in the state ; C. blandingii 
 var. acuta and C. hayi, 
 
 Cambarus blandingii var. acuta, Faxon. 
 
 Under the head of C. blandingii (Harlan) Faxon (loc. cit. 
 p. 19) has included a number of species decribed by other 
 authors as synonyms of this species. Faxon also forms a 
 variety ( C. blandingii var. acuta) under this species and in- 
 cludes under the variety a number of species and varieties 
 of other authors (loc. cit. p. 20.) This variety of C. bland- 
 ingii occurs in Missouri but has been reported from but one 
 locality, St. Louis. As to whether this species as found in 
 Missouri shows any peculiarities I cannot say for the only 
 specimens in the collection here came from Indiana. 
 
 Faxon says that the individuals of this species which are 
 collected in the Western States differ considerably from those 
 collected in the Southern States, and he considers the differ- 
 ences of the Western species from the Southern, characteris- 
 tic enough to form of the Western species a sub-variety 
 under C. blandingii var. acuta. 
 
 Cambarus hayi, Faxon. 
 
 C. hayi, as was mentioned above had only been reported 
 from Mississippi until April 10, 1897 when this species was 
 taken from James River, Mo. C. hayi is very clocely related 
 to C. blandingii but is easily distinguished from it by the 
 first pair of abdominal appendages of the male, the deeply 
 excavated rostrum and the shorter antennal scales. 
 
 Since C. hayi is not known except from two states and 
 only a few individuals have ever been taken, it would appear 
 that the species is not at all prolific. However, individuals 
 attain a very considerable size. The following are the 
 measurements of a first form, male. Length from tip of ros- 
 
 (8) 
 
trum to tip of telson 113 mm. ; length of carapace 56 mm.; 
 width of carapace 33 mm. ; length of hand 67 mm. ; length of 
 movable finger 36 mm. 
 
 GROUP II. 
 
 Cambarus gracilis, Bundy. 
 Plate III— Fig A 1? to A 5 and Bj to B 8 . 
 
 Only one species of Group II, C. gracilis, has been re- 
 ported from Missouri, and all specimens found belong to the 
 collection here. Most of them were found in the vicinity of 
 Columbia, although specimens have been taken near Mexico, 
 Audrain County. 
 
 Q gracilis, is one of the burrowing species and is seldom 
 found except during February and March. Then the fe- 
 males come from their burrows along the banks of creeks and 
 ponds, out into the water with their newly hatched young. 
 By the latter part of March the adults have returned to 
 their burrows. The young however may still be found in 
 the open water during April and May. 
 
 Faxon mentioned that among the hundreds collected 
 along the water-courses in the spring time, but few males 
 have been found. The same is true of the collection here. 
 From sixty-two adult specimens collected March 10, 1897, 
 only two are males, the larger of these being but 69 mm. in 
 length. Among the adult specimens taken in this vicinity 
 March 1899 not a single male was found. The collection 
 taken last spring, March 1900, contained no males. 
 
 However, this does not hold true for small specimens, for 
 out of fifty-two of the young, 25-35 mm. long, taken at the 
 same time and place as the sixty-two adult specimens, twenty- 
 seven were males and twenty-five were females. Also among 
 the young individuals collected in March 1899, I find as 
 many males as females. The same is also true of the collec- 
 tion for 1900. This shows that while they are young, males 
 are as plentiful as females and come from the burrows in as 
 great numbers. 
 
 Although C. gracilis is seldom found except in early 
 spring, I once found a solitary adult female in July, crawl- 
 ing across a clayey road just after a heavy rain. A solitary 
 adult male about 50 mm. in length was found at Columbia, 
 
 (9) 
 
under a log- in June 1897. Last summer August 1899, I capt- 
 ured two males in their' burrows. The burrows were out 
 on the open prairie some distance from any stream. 
 Those that I investigated were along a new road that was 
 being- graded. One of the workmen who happened to know 
 of my interest in crayfish noticed the burrows and told me of 
 them. He also said that the crayfish worked at night, for 
 during- the day the burrows were plowed over and their open- 
 ings stopped, but in the morning when he came out to work 
 the same holes were again opened up and surrounded by a 
 small heap of fresh earth. I determined to visit the burrows 
 myself. Accordingly, accompanied by my father and the 
 workman who had told me of them, I visited the burrows be- 
 tween eight and nine o'clock P. M., although many of the 
 burrows were found, in none of them did I find a crayfish 
 at work. It was decided to dig some of the burrows out. 
 The burrows descended vertically into the ground for about 
 four feet ; the main tunnel varying from an inch to an inch 
 and a half in diameter. The tunnel was terminated by a 
 flask-shaped enlarg-ement, the greatest diameter of which 
 was about six inches. This enlargement was partially filled 
 with mud and water. 
 
 Several burrows were dug out, but only two contained 
 crayfish, one in each. From one we took a male, and from 
 the other a female, each about 55 mm. in length. If the 
 crayfish came out at nig-ht, we must have been too early for 
 them, and since the earth which the workman found around 
 the mouth of the burrow in the morning was still moist, it 
 seems probable that they do their work towards morning. 
 
 C. gracilis has much the g-eneral form of C. diogenes of 
 the same region, except that it is smaller. The male appen- 
 dages differ considerably from those of C. diogenes; also the 
 annulus ventralis is quite different in the females of the two 
 species. In C. gracilis the annulus is movable and is dentic- 
 ulate on the anterior border, while in C. diogenes the annu- 
 lus ventralis is bounded anteriorly by two blunt tubercles. 
 Besides, the female C. gracilis lacks the battered appearance 
 that is characteristic of the old specimens of the female C. 
 diogenes. These differences easily distinguish the females 
 of the two species which are often found in company. 
 
 (10) 
 
C. gracilis does not attain as great a size as many other 
 species of Cambarus. The largest C. gracilis I have ever 
 seen does not exceed 82 mm, while it is not at all unusual to 
 see C. virilis and S. dio genes 120 mm. long. 
 
 The females differ from the males in having a shorter 
 hand and broader abdomen. A male of 69 mm. has a hand 30 
 mm. long- and 12 wide, while a female of 82 mm. has a hand 
 only 27 mm. long and 11 mm.wide. 
 
 Very little variation is to be noticed among adult indi- 
 viduals of C. gracilis. This may be due in part to the scar- 
 city of the male specimens for in all species the males show 
 much greater variation than the females. The fact that this 
 is a burrowing species and consequently less subject to vary- 
 ing- conditions than crayfish that do not burrow may to some 
 extent explain their uniformity of parts. Even in collections 
 of immature forms where males are numerous there is found 
 much less variation than among individuals of the same 
 ag-e belonging- to other species. C. virilis for instance, a 
 species which shows much individual variation. 
 
 As is well known, the young- Cambarus of any species 
 differs much in some of its parts from the adult forms. I have 
 had no opportunity to examine C. gracilis less than 7 mm. 
 in leng-th; but individuals 7 or 8 mm. long- show varations in 
 breadth of areola and length and shape of rostrum. At this 
 ag-e the rostrum is still short and bent down between the 
 eyes, as in the case with all newly hatched crayfish. How- 
 ever, in adult C. gracilis the rostrum is short as compared 
 with most species of Cambarus, and is bent downward be- 
 tween the eyes so that it fits closely over the antennules. I 
 attribute this form of rostrum to the burrowing- habits of the 
 species. 
 
 Specimens of C. gracilis 28-35 mm. long- are but little 
 different from mature forms, so far as g-eneral appearance 
 goes, but careful observation shows an important variation 
 from the adults in both males and females. The annulus 
 ventralis is not denticulate on the anterior border, nor does it 
 have the characteristic appearance from behind of two inter- 
 locked crescents; it is also much less grooved and convoluted 
 than in the adult female. In the adult males of this size, 
 
 (11) 
 
30-35 mm., the first pair of abdominal appendages are slen- 
 der and unarmed much as one would expect to find second- 
 form adult males; but Faxon says he has never seen a second- 
 form male C. gracilis, and from what I can learn none have 
 ever been reported. The antennal scale in the young- indi- 
 viduals is relatively broader and is truncate at the apex, and 
 also has the apical spine much shorter than in the adult. 
 Upon measurement there is found to be some variations in 
 relative lengths of cephalothorax and abdomen, although 
 not nearly so much as C. vi? His shows. 
 
 Below are measurements in mm., of twelve individuals; 
 the first column giving length of the body, the second, 
 length of abdomen, and the third length of cepalothorax. 
 
 BODY. 
 
 ABDOMEN. 
 
 CEPHALOTHORAX. 
 
 32.5 mm. 
 
 16.5 mm. 
 
 15.0 mm. 
 
 37.0 " 
 
 19.0 " 
 
 18.0 
 
 
 30.0 " 
 
 15.0 " 
 
 15.0 
 
 
 31.0 " 
 
 16.0 " 
 
 15.0 
 
 
 35.0 " 
 
 17.5 " 
 
 17.0 
 
 
 30.0 " 
 
 15.0 " 
 
 15.0 
 
 
 32.0 " 
 
 15.5 " 
 
 16.5 
 
 
 28.5 " 
 
 15.0 " 
 
 13.5 
 
 
 28.0 " 
 
 14.0 " 
 
 14.0 
 
 
 31.0 " 
 
 16.0 " 
 
 15.0 
 
 
 33.5 " 
 
 16.5 " 
 
 17.0 
 
 
 32.0 " 
 
 15.5 " 
 
 16.5 " 
 
 In noticing these varations it will be seen that the length 
 of the cephalothorax and abdomen is equal in some cases, 
 but that in the majority of cases the abdomen is longer than 
 the cephalothorax. Now there is also a variation in these 
 relative lengths in adult specimens, but instead of the abdo- 
 men in most cases being equal to or greater in length than 
 the cephalothorax the reverse is the casev as may be seen in 
 
 (12) 
 
the appended columns of measurements of the mature gracilis. 
 
 BODY. 
 
 ABDOMEN. 
 
 CEPHALOTHORAX. 
 
 70.0 mm. 
 
 35.0 mm. 
 
 35.0 mm. 
 
 54.0 " 
 
 25.0 " 
 
 29.0 ' 
 
 
 55.0 " 
 
 29.0 " 
 
 26.0 ' 
 
 
 79.0 " 
 
 39.0 " 
 
 40.0 ' 
 
 
 57.5 " 
 
 29.0 " 
 
 29.5 ' 
 
 
 50.5 " 
 
 24.5 " 
 
 25.5 ' 
 
 
 61.0 " 
 
 29.5 " 
 
 30.5 ' 
 
 
 57.5 " 
 
 29.0 " 
 
 28.5 ' 
 
 
 77.0 " 
 
 37.0 " 
 
 40.0 ' 
 
 
 69.0 " 
 
 34.0 " 
 
 35.0 ' 
 
 
 Faxon (loc. cit. p. 57) describes g. gracilis as having" 
 the abdomen shorter than the cephalothorax by the length 
 of the rostrum, but this cannot be said of the specimens 
 which I have at my command. Althoug-h a majority of those 
 measured show an abdomen shorter than the cephalothorax, 
 in most cases the cephalothorax does not exceed the abdomen 
 more than from 0.5 to 1.5 mm., which is not so much as half 
 the leng-th of the rostrum of a mature C. gracilis. 
 
 I have not yet been able to decide fully at what ag-e and 
 size C. gracilis becomes mature. But since the first pair of 
 abdominal appendages of the male and the annulus ventralis 
 of the female both have characteristic forms in the adults 
 which are quite different from the form of these organs in 
 the immature individuals, it occured to me that a graded ser- 
 ies of these appendages mig-ht be useful in determining- the 
 maturity of individuals. It may also serve as a guard ag-ainst 
 mistakes in classification, for if only immature forms of a 
 species are at hand one may class them as mature individuals 
 of a different species. 
 
 Plate III, — Figs. — A 1 to A 5 show a graded series of the 
 first pair of abdominal appendages of the male. Fig-. A t is 
 taken from a crayfish only 23 mm. long-. These appendag-es 
 show very little modification from the typical abdominal 
 appendage. Fig's. A 2 and A 3 show an increased modification, 
 and by the time the crayfish is 40 mm. in leng-th the appen- 
 dages have become modified as in Fig- A 4 . The crayfish may 
 
 (13) 
 
be adult at this stage. I have found females very little 
 larger, that were in berry. Fig. A 5 shows the appedages from 
 a male 67 mm. long. So far as I have been able to observe, 
 this figure represents the typical appearance of this pair of 
 appendages in the large male C. gracilis. 
 
 Plate III, Bj to B 8 show the modifications through which 
 the annulus ventrails passes during the growth of the female 
 C. gracilis. Fig. 'B 1 drawn from a specimen 20 mm. long, is 
 very simply formed, and the central depression is very slight. 
 The complexity of structure and increase in depth of central 
 depression gradualy increases with the age and size of the 
 animal, until the annulus ventralis of the larger females (Figs. 
 B 7 and B 8 ) presents a very complicated and characteristic 
 structure. Figs. Bj., as stated above, is taken from a spec- 
 imen 20 mm. in length; Fig. B 2 from one 22 mm.; Fig. B 3 , 
 27.5 mm.; Fig B 4 , 30 mm; Fig. B 5 , 35 mm.; Fig. B 6 , 36mm.; 
 Fig. B 7 , 50 mm.; and Fig. B 8 60 mm. 
 
 I think that Figs. B 7 and B 8 can both properly be 
 regarded as belonging to adult individuals, for I have found 
 females of C. gracilis not exceeding 40 mm. that were in berry. 
 
 However, Fig. B 8 can be considered the more typical form 
 of the adult annulus ventralis of the female C. gracilis. 
 
 One other point should perhaps be mentioned before 
 leaving the consideration of this species. That is concerning 
 their moulting season, which so far I have been unable to 
 determine. 
 
 As is well known young crayfish of any species have no 
 particular, well-defined moulting season, but may moult at 
 almost any time during the year. This is no less true of C. 
 gracilis than of other species. However, of the adult forms 
 I have been entirely unable to find one moulting at any 
 period whatever. 
 
 It is impossible that the moult should have taken place 
 before the spring collections were made, for often the females 
 that were captured had the newly hatched young still 
 clinging to the swimmerets. Besides, amoung those that 
 carried no young there was no sign of a recent moult. 
 
 I have kept them through the summer and far into the 
 following winter without a molt occuring. The specimens 
 mentioned above which were taken from their burrows in 
 
 (14) 
 
August, were kept through the fall, winter and the following 
 spring, when they died without having moulted. 
 
 C. gracilis has been under observation at all seasons of the 
 year, but I have not seen one over 30 mm. in length pass 
 through a moult. Laboratory conditions might retard their 
 moulting, but it is improbable that these conditions should pre- 
 vent moulting. C. gracilis thrives under laboratory treatment, 
 and is hardier and more easily kept alive than some other 
 species. 
 
 In experimental work on the appendages of crayfish I 
 found the young of C. gracilis to grow more rapidly and with- 
 stand mutilation as well if riot better than the young of C. virilis. 
 
 GROUP III. 
 
 Cambarus bartonit, Girard. 
 
 For synonymy see Faxon (loc. cit. pp. 59, 60.) 
 
 Faxon (loc. cit. p. 61) mentioned C. bartonii as probably 
 belonging to Missouri, but, although several new species have 
 been discovered in the state since that date, this species has not 
 been found. 
 
 C. bartonii is taken as a type of Group III. It has a wide 
 geographical distribution, and, as might be expected, is subject 
 to much variation. These variations affect especially the 
 rostrum, chelae, areola, antennal scales and epistoma. In the 
 common Eastern form the rostrum is short, broad, and almost 
 plane above, the sides nearly parallel from the base almost to 
 the tip, where they suddenly converge to form the short 
 acumen. The chelae are coarsely punctate, the inner margin of 
 the hand sub-tuberculate, and the fingers gaping at the base. 
 The areola is quite narrow, and the antennal scale is narrow. 
 
 The Western specimens have a longer, narrower rostrum, 
 the margins of which converge gradually to form a longer 
 acumen. The areola is wider, and the antennal scale broader 
 at the base. The chelae are smoother and in some individuals 
 bearded at the base. 
 
 Although the extreme Western forms differ much from the 
 extreme Eastern, there are so many intermediate gradations 
 between them that Faxon does not consider it justifiable to 
 classify these extremes as different species. 
 
 C. bartonii is the only eyed species that is known to inhabit 
 Mammoth Cave. It is found there in company with a blind 
 
 (15) 
 
species, C. pellucidus, a member of Group I. Some writers have 
 been led to conclude, by finding C. bartonii in company with the 
 blind species, that C. pellucidus has been directly derived from 
 C. bartonii, but Faxon, after a careful comparison of likenesses 
 and differences of the species, and in consideration of the fact 
 that the general characteristics of C. pellucidus (Tellk.) place it 
 in Group L, suggests that it is probable that the origin of the 
 blind species dates much farther back than would be possible 
 were it derived from C. bartonii. He says (loc. cit. p. 42) : " The 
 simple form of the male appendages and the combination of 
 characteristics belonging to different groups seen in C. pellucidus 
 indicate to my mind that it is a very ancient form, which has 
 been preserved in the seclusion of the cave while its nearest 
 kin succumbed to the sharper struggle incident to life outside, 
 or were replaced by modified descendants evolved to meet the 
 changeable conditions which obtain without the caverns. This 
 view is rendered more probable when one remembers that this 
 same blind form C. pellucidus occurs in the Wyandotte Cave on 
 the other side of that ancient river, the Ohio. The transpor- 
 tation of an eyeless species from the Kentucky caverns to those 
 of Indiana seems out of the question, and one is driven to the 
 conclusion that the subterranean waters of both localities 
 derived this eyeless species from a simpler form with well- 
 developed eyes, that peopled the streams throughout this region 
 at a remote period." 
 
 Cambarus setosus, Faxon. 
 
 Although C. bartonii and C. pellucidus can not be regarded 
 as closely allied species, there are two blind species of the 
 Bartonii Group for which a close relationship can be claimed. 
 These are C. hamulatus and C. setosus. The latter has been 
 reported from Jasper County, Missouri, but from no other 
 locality. It was first named and described by Faxon ('89). 
 Miss Ruth Hoppin collected this species from Wilson's Cave 
 and wells in the central part of Jasper County. Samuel Gar- 
 man ('89) quotes from letters of Miss Hoppin a description of 
 the wells and cave. I reproduce a part of the description here : 
 
 " The cave is about fifty feet long and nearly as wide, oven- 
 shaped and high enough to stand in, except around the sides. 
 * * * A small, very clean stream flowed along the left side, 
 having a width of two feet and a depth of three, with tempera- 
 ture of plus 54 F. About ten feet from the entrance the light 
 
 (16) 
 
struck the stream in such a manner that we could see everything 
 in the water without a lantern. The first things that caught 
 the eye were a lot of crayfish, a dozen in all, like those I took 
 from the wells. It seemed as if I might take every one of them. 
 But though blind they have one or more of the other senses 
 very keenly developed. I am very sure that they, as well as 
 the white fishes, have the tactile sense developed to an unusual 
 degree. At the least touch upon the water they dart away. 
 * * * The crayfish were all found near the entrance, where 
 there is considerable light. * * * I concluded that the 
 crayfish liked the light. Perhaps they remain near the entrance 
 because there they find a supply of food. From one well thir- 
 teen blind crayfish were taken, from another two, and from 
 another one. * * * One well, an artesian, went dry when 
 a neighbor dug another farther down the hill. It was found 
 that the first well opened at the side directly into a small cave. 
 All these are in limestone ; only in this formation is good water 
 to be obtained hereabout. The larger caves in this vicinity are 
 under the limestone cliffs and hills that skirt Centre Creek. 
 The wells are usually walled with stones that leave spaces 
 through which the fishes may pass. There are probably many 
 small subterranean springs and streams, not one underlying 
 lake, as popular belief has it." 
 
 Garman (loc. cit. p. 231) says of these caves that " It is 
 evident from the notes that these caves are numerous and sim- 
 ilar to those in the same formation in other states." 
 
 Besides the crayfish, several other species of animals were 
 found in the caves and wells, and Garman feels sure that further 
 collecting will reveal several other interesting forms. Of the 
 Crustacea he says (p. 235) : " In part, at least, the problem of 
 the origin of the cave Crustacea is simplified by the fact that 
 they are so distinct in various caves as to leave no doubt that 
 they are descended from ancestors already of different species 
 at the time of entering subterranean habitations. The blind 
 crayfish of the Missouri caves is very distinct from any previ- 
 ously known; it is described under the name Cambarus setosus. 
 The common species of the neighborhood, C. virilis, is also 
 found to enter the underground retreats, but it is not of the 
 outside forms, the nearest ally of the blind form. The latter 
 bears so close an affinity to C. bartonii as to suggest derivation 
 from it. A somewhat parallel condition exists in the caves of 
 Missouri and those of Kentucky. In these last, with the blind 
 
 (17) 
 
C. pellucidus we find C. bartonii, the nearest ally of the blind cray- 
 fish in Missouri, C. setosus, and with the latter again in the 
 Missouri caves is found an eyed species, C. virilis, more nearly 
 allied to the blind one in the Mammoth Cave. The relationship 
 existing between the species C. setosus and C. bartonii is much 
 closer than between C. pellucidus and C. virilis. A distribution 
 of C. bartonii covering so large a portion of the Upper Missis- 
 sippi Valley to some extent favors the idea of the derivation 
 from it of C. setosus. The greater difference between C. pellucidus 
 and all known eyed species points towards a longer subjection 
 of that form to the spelaean influences." 
 
 C. hamulatus (Cope, Faxon), the blind species from Nicka- 
 jack Cave, Tennessee, stands between C. setosus and C. pellucidus, 
 but nearer to C. setosus. C. hamulatus, however, does not occur 
 in Missouri. 
 
 Cambarus ayersii, n. sp. 
 Plate V., Fig. A. 
 
 In 1897 Dr. Howard Ayers found in the stream in Fisher's 
 Cave, near Springfield, Missouri, a species of blind crayfish 
 which belongs to the C. bartonii group, and in some respects 
 resembles C. setosus very closely, yet it differs much in others. 
 On account of these differences it is here described as a new 
 species. 
 
 Male, form II. — Rostrum medium length, shorter than the 
 antennal scales, slightly concave above, with short acute lateral 
 spines ; acumen triangular, acute. Postorbital ridges short, 
 terminated by an acute spine. Carapace subcylindrical, flat- 
 tened and smooth above; portion of carapace behind cervical 
 groove very long; sides of carapace behind cervical groove 
 coarsely granulate, in front of cervical groove finely spinulate ; 
 branchiostegian spine short, acute, antennae slender and longer 
 than the body. Hand long and slender, inner border orna- 
 mented with a row of small, sharp tubercles. Carpus slender, 
 with deep indentation on dorsal surface, inner margin with four 
 sharp spines, lower surface with two sharp spines. Upper 
 margin of the meros subdentate, lower surface of meros fur- 
 nished with sharp spinules arranged bi-serially. Upper surface 
 of the basal segments of the antennules ornamented by tufts of 
 rather long setae. Third pair of legs hooked. First pair of 
 abdominal appendages fashioned after the type of C. bartonii 
 Group; short, articulated at the base, dilated in the middle; 
 
 (18) 
 
tips bifid, ending in two short recurved corneous hooks which 
 are closely approximated, the outer hook being visible from the 
 median aspect, tip of the inner hook slightly attenuated. A few 
 fine setae. 1 are scattered on the dorsal aspect of the abdomen. 
 
 Measurements of Male, form II. — Length from tip of ros- 
 trum to posterior border of telson, 66 mm. ; length of cephalo- 
 thorax, 32 mm. ; length of abdomen, 34 mm. ; length of rostrum, 
 45 mm. ; length of antennae from base of antennal scale to tip, 
 89 mm. ; length of hand, 32 mm. ; breadth of hand, 9 mm. 
 
 The chief differences between this species and C. setosus lie 
 in the presence of postorbital ridges, postorbital spines and 
 rostral spines, which are well developed in these specimens, 
 while they are described as absent in C. setosus; also in the 
 breadth of areola. C. setosus is described as having a narrow 
 areola, while in this species it is strictly linear. Then again, 
 the first pair of abdominal appendages are not like those 
 described for C. setosus. Garman (loc. cit. PI. I.) figures and 
 describes the first pair of abdominal appendages of the male 
 C, setosus, and, although he figures three different forms that 
 these appendages may take, none of them correspond to the 
 form of appendage found on the species C. ayersii. 
 
 From the figures and description of Garman it is certain 
 that this species is not C. setosus. 
 
 Since writing the above I have received from Dr. C. Thorn 
 a small (31 mm. in length) living specimen of blind crayfish 
 which was taken from a well sixty feet in depth at Joplin, Mis- 
 souri. It is not unusual to find these blind crayfish in that 
 vicinity. 
 
 It had been kept a week or two before I was able to make 
 observations on its behavior in confinement. I can get no 
 evidence that the rudimentary eyes are sensitive to light or are 
 more sensitive to touch than other parts of the body. When 
 placed in a glass jar with paper on one side it hides on the shady 
 side. This crayfish lived but a short time, and was not active 
 in captivity. It was almost colorless, and the carapace was 
 translucent. Wilson's Cave, where C. setosus is found, is not 
 more than fifteen or twenty miles from Joplin. 
 
 In many respects this specimen accords with the descrip- 
 tion of C. setosus. In others it differs from C. setosus, yet not 
 more than could be accounted for by its small size and the fact 
 that it is a female. As is well known, even among eyed crayfish 
 the females alone are not sufficient to satisfactorily determine 
 a species. 
 
 (19) 
 
C. setosus is described as having antennae as long or longer 
 than the body. In this specimen they are considerably shorter. 
 The chelae have very much the general shape described for 
 C. setosus, but are scarcely spiny at all, and are less setose. 
 Again, the areola could not well be described as narrow, for it 
 is of medium width : but this may be due to its being a young 
 specimen, for the areola in immature crayfish is proportion- 
 ately broader than in adults. 
 
 Miss Hoppin states that among living specimens the young 
 C. setosus are not so white as the older ones, and she also says 
 that the specimens became opaque when placed in alcohol, 
 although in life they are so transparent that the movements of 
 the internal organs can be seen. In this specimen, which has 
 now been in alcohol five months, I can not see that its color or 
 transparency has been materially altered from what it was in 
 life. The part of the carapace in front of the cervical groove 
 is still so transparent that, with a magnification of ten diameters, 
 the fibers of the gastric muscles and the cceca of the hepatic 
 gland can readily be seen. 
 
 This specimen differs still more from C. ayersii than from 
 C. setosus. The general contour of the body resembles that of 
 C. ayersii, but the relative lengths of the abdomen and cephalo- 
 thorax differ more, the abdomen being 3 mm. longer than 
 cephalothorax, while in C. ayersii it is only 2 mm. longer. 
 Again, in C. ayersii the antennae are much longer than the body, 
 while in this specimen they are not so long. The hand is not 
 spiny, and only very sparsely setose. The carpus is without 
 the conspicuous indentation on its dorsal surface found in 
 C. ayersii, and has but one spine on the lower surface and one 
 on the inner border. The lower border of the meros has a 
 double row of very fine spinules. The rostrum is more concave 
 than in C. ayersii. and the rudimentary eyes less completely 
 hidden underneath it. The antennal scales are longer than the 
 rostrum. 
 
 Altogether, I consider that this small specimen shows more 
 points in favor of C. setosus than in favor of C. ayersii. 
 
 CAMBARUS DIOGENES, GlRARD. 
 
 For synonymy see Faxon ('89, p. 71). ~ 
 
 This species has a widespread distribution over the United 
 States. It extends north to the Great Lal^es, south to the 
 Gulf, east to the Atlantic coast and west to the Rocky Moun- 
 
 (20) 
 
tains. In Missouri it has been found in Carroll, Boone and 
 St. Eouis Counties. In the general form of its body and in its 
 habits it resembles C. gracilis, and is often collected in company 
 with this species. In one collection are five crayfish taken at 
 the same time from Rollin's Pond, near Columbia. Of these 
 five specimens, two are large first-form males of C. diogenes; 
 the other three are medium-sized females of C. gracilis. Unlike 
 the males of C. gracilis, the males of C. diogenes are found in as 
 great abundance as the females. 
 
 In discussing C. gracilis I have mentioned the resemblances 
 between these two species. Specimens of C. diogenes from the 
 same locality vary much. In some the rostrum is deeply exca- 
 vated. The rostrum of the females is bent down at a greater 
 angle than the rostrum of the males. In the females the abdo- 
 men is noticeably broader and flatter than in the males. This 
 is true to some extent of all species, but it is more pronounced 
 in C. diogenes than in any species I have studied. 
 
 Faxon says the Western specimens are larger than the 
 Eastern ones. He also notes other differences between the 
 Eastern and Western specimens. In individuals from the East 
 the areola is not completely linear, the rostrum is narrower, and 
 the epistoma narrower than in individuals from the West. He 
 considers these specimens sufficiently different from the West- 
 ern form to be classed as a variety, and he calls them C. diogenes, 
 ludoviciana. 
 
 C. diogenes is pre-eminently a burrowing species. It is 
 often found at a great distance from surface water, as in stream, 
 in meadows and cornfields. 
 
 Several accounts of their burrows and mud chimneys have 
 been written. Audubon ('44) is the first to figure and describe 
 the mud chimneys built by C. diogenes. His description of them 
 is in connection with his description of the ingenious manner in 
 which the White Ibis draws the crayfish from its hiding place. 
 
 Girard ('52) has also given an account of their burrows and 
 chimneys. His observations were made in the vicinity of Wash- 
 ington, D. C. A part of his description I quote here : " The 
 holes as they appear at the surface of the ground are nearly 
 circular, and vary from seven-tenths of an inch to an inch and 
 a half in diameter. The depth of the burrows varies with the 
 location ; these we generally found to be from sixteen inches to 
 two feet, and sometimes to three feet and more. * * * 
 From the surface of the ground the excavation exhibits a 
 gradual slope, in direction more or less undulating, for a dis- 
 
 (21) 
 
tance from five to ten inches, when it becomes vertical for 
 six or eight inches, and then terminates in a sudden bottle- 
 shaped enlargement, in which the animal is found. The bottom 
 of the burrow having no subterranean communication, no other 
 issue except towards the surface, it is entirely isolated from its 
 neighbors and leaves no chance for escape to its inhabitants. 
 The same burrow may have several external holes connected 
 with it, several inclined channels, which, however, meet at the 
 depth where it becomes vertical. We found constantly the 
 cavity full of water, but this was in March and April. The 
 bottom for several inches was filled with soft, pulpy mud. 
 
 " There are other instances of burrows somewhat more 
 complex. Their direction may be oblique throughout their 
 whole extent, and composed of a series of chambers or ovoid 
 enlargements succeeding each other at short intervals. Some- 
 times, also, and connected with one of the chambers, a narrow 
 and nearly tubuliform channel extends downward to a much 
 greater depth, and appears to us as a retreat either during the 
 cold winter or else during the dryness of summer, when the 
 water is low. That it is not for the mere purpose of escaping 
 pursuit we infer from the fact that we repeatedly caught the 
 animals in the chambers above, where they remained quietly 
 instead of attempting to disappear into the compartments below. 
 
 " In the spring, and, we are told, in the fall also, the burrow- 
 ing crayfish builds over the holes of its burrow a chimney of the 
 maximum height of one foot, but most generally lower. The 
 chimney, circular-pyramidal in shape, is constructed of lumps of 
 mud varying in size, irregularly rolled up and piled up, one upon 
 each other, and intimately cemented together. Its exterior 
 has a rough and irregular appearance, whilst the interior is 
 smooth and as uniform as the subterranean channel having the 
 same diameter." 
 
 Girard stated that the crayfish worked at night, but that he 
 had never been able to see the animal at work. However, since 
 that time Dr. Abbot ('95) has published a paper in which he 
 states that his nephew, Mr. Joseph De B. Abbot, has seen the 
 crayfish engaged in building its chimney. The observation was 
 made at night by the light of a candle. The crayfish was seen 
 to emerge partially from its burrow, bearing " on the back of 
 its right claw a ball of clay mud which, by a dextrous tilt of the 
 claw, was placed on the rim of the chimney.^ Then the crayfish 
 remained perfectly quiet for a few seconds, when it suddenly 
 
 (22) 
 
doubled up and dropped to the bottom of the burrow. There 
 elapsed some three or four minutes between each appearance, 
 but every time it came it brought a ball of clay and deposited 
 it in the manner I have described. About two-fifths of the balls 
 were not placed with sufficient care, and rolled down the outside 
 of the chimney." 
 
 Besides the descriptions of the habits of these burrowing 
 crayfish which I have already quoted, I may also mention 
 papers by R. S. Tarr ('84) and Dr. C. C. Abbot ('84). 
 
 Tarr believes that the chimneys are merely the result of the 
 excavation of the burrows, a sort of accidental accompaniment, 
 and imply no design on the part of the crayfish. On the other 
 hand, Dr. Abbot believes them to be due to a definite and care- 
 fully executed purpose on the part of their architects. They 
 are often built on the steep banks of ditches, where the ejected 
 mud would surely roll into the ditch if not carefully arranged 
 to prevent it. In several instances observed by Dr. Abbot, 
 where the chimneys were built on sloping banks, the base of 
 the chimney was provided for by leveling the ground before 
 the foundation of pellets of mud was laid. From observations 
 made on forty of these towers or chimneys, Dr. Abbot is con- 
 vinced that not one of the forty could be the result of accident. 
 
 From the observations made up to this time, no one has 
 been able to give a satisfactory explanation as to the object in 
 building these elaborate burrows and the seemingly carefully 
 erected towers. More knowledge concerning the winter habits 
 of the animal, and its mode of life during the breeding season, 
 would perhaps throw light upon the purpose of the towers and 
 burrows. 
 
 C. dio genes is not plentiful in Central Missouri, and in this 
 region the mud chimneys are built about eight inches high, and 
 are formed of pellets of mud of regular size and shape. On the 
 inside the chimneys are plastered smooth, and outside they have 
 the characteristic rough appearance due to being formed of 
 mud balls. 
 
 GROUP IV. 
 
 The remaining species of crayfish found in Missouri belong 
 to Group IV. 
 
 A male of this group is easily distinguished from one of 
 any other group by the form of the first pair of abdominal 
 appendages, which are more slender than in any other, and in 
 the first-form males they are always terminated by two slender 
 
 (23) 
 
and, in most species, nearly straight styliform tips. 
 
 Beginning with the species which is least plentiful in this 
 state, I shall treat of the members of this group in the order of 
 their abundance. 
 
 Cambarus harrisonii, Faxon. 
 
 This species has been reported from but one locality in the 
 state, Irondale. We have no specimens in the collection here. 
 Faxon (loc. cit. p. 95) says that C. harrisonii resembles 
 C. rusticus in general form, but that the first pair of abdominal 
 appendages of the male and the annulus ventralis of the female 
 differ conspicuously from any other species of the group. 
 Faxon figures the first pair of abdominal appendages very short 
 and thick; the rami short, rather blunt and slightly curved. 
 These appendages would suggest a close relationship with 
 Group III. C. harrisonii is probably a border species. No 
 second-form males have been reported. 
 
 Cambarus whitman i, n. sp. 
 Plate V., Fig. B ; Plate III., Figs. Ci and C2. 
 
 This crayfish was taken from the James River, Missouri, 
 on August 20, 1897. It appeared at first to be a variation of 
 C. palmeri (Faxon), but upon careful examination I find that it 
 differs in important distinguishing characteristics. No other 
 species has been described with which this species can be 
 identified. 
 
 Male, form II. — Rostrum long, deeply excavated, margins 
 nearly parallel from base to lateral spines, which are acute, 
 short and corneous ; acumen long. Postorbital ridge termi- 
 nated by a blunt spine. Carapace punctate above and granulate 
 on the sides ; lateral spine large ; portion behind cervical groove 
 flattened on top. Areola very narrow, with a small anterior and 
 large posterior triangular field. The length of the areola is 
 one-half the distance from the cervical groove to the tip of the 
 rostrum. Abdomen broad, as long as the cephalothorax. 
 Proximal segment of the telson bispinous on each side, distal 
 segment slightly concave on posterior border. Antennae long; 
 laminae slightly longer than the rostrum, broadest in the middle, 
 tapering to a short spine at the apex. Third maxillipeds hairy 
 within. Anterior process of the epistoma notched at the apex. 
 Chelae long, smooth and punctate, margined on the outer edge. 
 Hand straight, inner margin straight and short, with a double 
 
 (24) 
 
row of small ciliated tubercles. Fingers long and straight, 
 with corneous incurved tips, punctate and ciliate above. Mov- 
 able finger furnished with a double row of ciliated tubercles 
 on basal half of the outer edge. Outer finger hairy below at 
 the base. Opposable edges of the fingers bluntly tuberculate. 
 Carpus with three spines on interior border; smooth below, 
 with two prominent anterior spines. Meros with two spines 
 on upper surface, outer row of inferior biserial spines reduced 
 to two well-developed spines, large sharp spine on anterior 
 border. Third pair of legs hooked. First pair of abdominal 
 appendages articulated at the base, stout, long and straight, 
 bifid for a short distance from the tip, rami divergent, outer one 
 the longer. 
 
 Below are given the measurements of a large male, form 
 II. : Length from tip of rostrum to tip of telson, 120 mm. ; 
 length of rostrum, 14 mm. ; breadth of rostrum at the base, 
 5.5 mm. ; length from tip of rostrum to cervical groove, 40 mm. ; 
 length of areola, 20 mm. ; breadth, 1 mm. ; outer margin of 
 hand 68.5 mm., inner margin 15 mm.; movable finger, 49 mm. 
 
 This species is closely related to the recently described sub- 
 species C. palmeri longimanus (Faxon); in some particulars it 
 resembles it more than C. palmeri. But the shape of the hand 
 and the first pair of abdominal appendages is so different that 
 they can not belong to individuals of the same species. 
 
 Plate III., Figs Ci and C2 show the hand and first pair of 
 abdominal appendages of the male of C. whitmani, whose meas- 
 urements are given above. The hand is drawn natural size and 
 the appendages one-half longer than natural size. 
 
 Plate VI., Fig. 2 is reproduced from a photograph of the 
 same individual from which the hand and abdominal appendages 
 are. drawn. 
 
 Cambarus immunis, Hagen. 
 
 Plate III., Figs. Di to D3, Ei to E3. 
 
 For synonomy see Faxon ('89, p. 99). 
 
 Until recently this species had been reported from only one 
 locality in the state, St. Louis, During the period covered by 
 my studies it has been collected from a number of localities in 
 the northern part of the state. We have in the collection here 
 specimens from St. Louis ; Mexico, Audrain County ; Canton, 
 Lewis County; Chillicothe, Livingston County; Martinston, 
 Putnam County, and from St. Joseph. 
 
 (25 
 
This species inhabits ponds and creeks, and in rainy weather 
 individuals are often found crawling freely about in the meadows 
 and fields and along the roads. 
 
 In typical specimens C. immunis has a rostrum without 
 latent teeth, but it is not unusual to find, especially in young 
 individuals, small rostral spines. 
 
 Our collection of C. immunis contains seventy-five or eighty 
 specimens, too small a number to base a study of variation 
 upon. However, the following differences have been noted : 
 
 Plate III., Fig. Di shows the chelae, first pair of abdominal 
 appendages and the rostrum of a first-form male 67 mm. in 
 length. Hand with curved external border, movable finger 
 with characteristic notch on the inner border; base of fingers 
 densely setose. Two spines on internal border of carpus, one 
 spine on upper surface of meros. Rostrum triangular and 
 sharp-pointed. Abdominal appendages small, curved and with 
 scattering seta? on the proximal half of the internal border. 
 
 Plate III., Fig. D2 shows chelae, rostrum and first pair of 
 abdominal appendages of a first-form male 73.5 mm. in length. 
 This specimen is from the same locality as the specimen of 
 Fig. Di. The hand is long, narrow and straight and without 
 the notch at the base of the movable finger. The carpus has 
 two spines on the inner border. Meros is destitute of spines 
 on upper surface. The setae are less developed, both on the 
 chelae and on the abdominal appendages, than on the specimen 
 of Fig. Di. The rostrum is broader and more sharply pointed. 
 This claw without a notch is, I think, a regenerated one. I 
 infer this from the fact that in several instances I have found 
 individuals upon which the claw on one side was without the 
 notch, while the one on the other side had the notch. In every 
 instance where this is the case the claw without the notch is the 
 smaller of the two. I have also found specimens where both 
 chelae were devoid of the notch. On the same hypothesis I 
 take it that in such cases both chelae have been taken off, and 
 that these straight claws are regenerated ones. This view is 
 borne out by the fact that such claws are always undersized 
 for the individual. I have not observed the regeneration of 
 a c'helae in C. immunis, but in C. virilis the regenerated claw 
 passes through at least two moults before it takes on the 
 appearance of a normal claw. The notched or hooked appear- 
 ance of the claw of C. immunis is mainly due to the presence of 
 two or three large tubercles above the base of the inner margin 
 of the movable finger. In regenerated claws of C. virilis the 
 
 (26) 
 
usual spines and tubercles are not always present, and then only 
 after two or three moults. This may also be the case in 
 C. immunis. Judging from the size of the unnotched claws 
 sometimes found upon individuals of C. immunis, several moults 
 have certainly taken place since the original chela was lost. 
 
 Plate III., Fig. D3 shows the chelae, rostrum and first pair 
 of abdominal appendages of a first-form male 71 mm. in length. 
 The right hand shows the notch, and the left one is without it. 
 It is noticeable, also, that the setae are better developed on the 
 right hand than on the left. Each carpus shows two spines ; 
 on the right meros and one inconspicuous spine on the 
 left one. Rostrum with concave edges. Abdominal append- 
 ages slender and less curved than in typical specimens ; setae 
 on median border. 
 
 There are some constant differences between the first and 
 second-form males. The hand of a second-form male is always 
 relatively much smaller than of a first-form male. It is shorter, 
 narrower and thinner, and the spines and setae are less devel- 
 oped. The following are the measurements of the chelae of two 
 specimens each, of first-form and second-form males : 
 
 First-form male : Length, 71 mm. ; length of outer margin 
 of hand, 33 mm., length of inner margin 31 mm., breadth 11 mm. 
 
 Second-form male: Length, 71.5 mm.; length of outer 
 margin of hand 25.5 mm., length of inner margin 24 mm., 
 breadth 8 mm. 
 
 First-form male : Length, 59 mm. ; length of outer margin 
 of hand 26 mm., length of inner margin 24.5 mm., breadth 9 mm. 
 
 Second-form male : Length, 61 mm. ; length of outer 
 margin of hand 19 mm., length of inner margin 18 mm., breadth 
 6.5 mm. 
 
 Plate III., Figs. El and E2 show the chelae (natural size) 
 of the specimens from which the first pair of measurements 
 were taken. In general, the rostrum of the first-form male is 
 less excavated than that of the second form. In some first-form 
 males the rostrum is nearly plane, but it is usually slightly 
 excavated. 
 
 The female C. immunis has the abdomen noticeably broader 
 than the male, so much broader, in fact, that the sexes can be 
 recognized at a glance by this one feature. The hand of the 
 female is also relatively much shorter. A comparison of Figs. 
 El and E3 of Plate III. will show the relative proportions of the 
 hands of the male and female. Fig. El is a chela of natural size 
 from a first-form male, 71 mm. in length. Fig. E3 is a chela, 
 
 (27) 
 
also natural size, from a female 80 mm. in length. The species 
 are no better developed on the hand of the female than on the 
 hand of the second-form male, but it is thick and short instead 
 of thin and narrow. 
 
 Cambarus rusticus, Girard. 
 
 Plate III., Figs. 1 to 13. 
 
 This species is widely distributed over the United States, 
 and has been reported from several localities in Missouri. In 
 the collection we have specimens from the Osage River, Spring- 
 field, Marshalfield, Mt. Vernon, Linn Creek, and perhaps 
 Columbia. Several individuals of C. rusticus were found in a 
 large collection of alcoholic specimens of C. virilis taken at 
 Columbia, but whether they were captured with the C. virilis 
 or were introduced into the collection is uncertain. The species 
 is not common in the locality. 
 
 Faxon ('85, pp. in, 112) suggests that under C. rusticus, 
 C. placidus (Hagen), C. juvenilis (Hagen), and also C. wiscon- 
 siensis (Bundy), should be included. He says of the above 
 mentioned species : " After a careful comparison of all the 
 species before me, I am inclined to unite them all as forms of 
 C. rusticus" 
 
 As would be inferred from this, C. rusticus is subject to 
 considerable variation. Faxon mentions variations in the chelae, 
 rostrum and first pair of abdominal appendages ; also variations 
 in the shape of the areola. He gives the type description of the 
 hands, as follows : " Fingers gaping at the base, not bearded ; 
 movable finger incurved, external margin convex." However, 
 individuals with external margin of the hand straight are not 
 unusual." Faxon also mentions that in a collection of C. rus- 
 ticus from Yellow Springs, Ohio, the young specimens, about 
 20 mm. long, have a dense beard on the inner side of the 
 external finger, near the base. The rostra of all the individuals 
 agree in being excavated, and in having thickened margins ; but 
 the rostra may be long or short, with or without rostral spines, 
 and may sometimes have a median carina near the tip. Faxon 
 speaks only of young specimens as having rostral spines. The 
 first pair of abdominal appendages are usually- straight and of 
 medium length, but in some individuals these appendages are 
 found to be considerably curved and longer than the type speci- 
 mens. The areola is usually of moderate width, with sides 
 parallel for a part of its length; but in some specimens the 
 
 (28) 
 
areola is narrow at a point in front of the center, and conse- 
 quently its sides are not parallel. 
 
 Besides the above mentioned variations described by 
 Faxon, the individuals which 1 have examined show other 
 departures from the type description. 
 
 C. rusticus is described as having an areola equal in length 
 to the distance of the cervical groove from the base of the ros- 
 trum ; an abdomen a little shorter than the cephalothorax, and 
 the anterior process of the epistoma blunt. In the specimens 
 before me the areola is uniformly shorter than the distance from 
 the cervical groove to the base of the rostrum, and instead of 
 the abdomen being shorter than the cephalothorax, the reverse 
 is the case ; the epistoma, instead of being merely blunt, is often 
 slightly notched. 
 
 The variations among individuals of the collection are so 
 marked that without a series of specimens ranging from 25 to 
 100 mm. in length, the species would be very hard to identify. 
 But with a series of specimens collected at the same time and 
 place, one can not fail to see that they all belong to the same 
 species. 
 
 With only a few individuals to study, one might easily 
 classify members of this species as C. medius (Faxon), or C. neg- 
 lectus (Faxon). In a number of characteristics C. rusticus and 
 C. medius are identical. The features by which C. rusticus is to 
 be distinguished from C. medius are differences in the rostra, in 
 the length of the first pair of abdominal appendages, the relative 
 length of abdomen and cephalothorax, and the areolae. 
 
 In certain individuals of C. rusticus the rostrum is broad, 
 without spines and with a median carina near the tip. The 
 carina makes the rostrum answer to the description of the ros- 
 trum of C. medius. The chief difference between the abdominal 
 appendages of the two species is that in C. medius the rami are 
 longer than in C. rusticus. Whenever the rami of C. rusticus 
 are a little lengthened, we have the C. medius form of appendage. 
 C. rusticus is described as having an abdomen a little shorter 
 than the cephalothorax, while C. medius is described as having 
 an abdomen and cephalothorax of equal length; but in the 
 specimens which I have, the abdomen is uniformly longer than 
 the cephalothorax, so that this can not be used as a character 
 by which to distinguish the species. 
 
 I was at first inclined to identify them all as C. medius. 
 However, at the suggestion of Dr. Ayers, under whose direction 
 I have clone the work, I sent several individuals to Professor 
 
 (29) 
 
Faxon in order to get his opinion as to what specific name 
 should be applied to them. I sent two large ones and three 
 small ones. Faxon classified them as two species, a thing which 
 I think he would not have done had he had a complete series 
 before him. His classification is C. rusticus and C. neglectus. 
 Here again the chief features distinguishing these two species 
 are shape of rostra and relative length of abdomen and cephalo- 
 thorax ; the first pair of abdominal appendages and the develop- 
 ment of spines on the lower surface of the meros. As already 
 noted, the rostrum is quite variable ; in the specimens before me 
 there are all gradations between the form of rostrum described 
 for C. neglectus and that described for C. rusticus. C. neglectus 
 is also described as having an abdomen larger than the cephalo- 
 thorax. This is true of all the specimens before me, not only of 
 the specimens described as C. neglectus, but also those described 
 as C. rusticus. The first pair of abdominal appendages of the 
 first-form male of C. neglectus are described as nearly straight 
 and so long that when turned forward the tips of the rami reach 
 the base of the chelae. These appendages in C. rusticus are also 
 nearly straight, but are only long enough to reach to the base 
 of the second pair of legs. A slight decrease in the length of 
 the rami of C. neglectus is all that is necessary to reduce them to 
 the C. rusticus form. In one of the specimens that Faxon 
 classified as C. neglectus these appendages are no longer than 
 demanded by the description of C. rusticus. In C. neglectus the 
 lower surface of the meros is described as having two rows of 
 spines ; in C. rusticus all of these inferior biserial spines are 
 described as only slightly developed, except the apical one of 
 each row. More often than not, these spines in the species 
 described as C. neglectus are reduced to low blunted tubercles, 
 thus bringing them to the C. rusticus form. There is one more 
 point that should be mentioned, viz. : in C. rusticus the antennal 
 scale is described as slightly longer than the rostrum, while in 
 C. neglectus the antennal scale is described as equal in length to 
 the rostrum, but in the individuals described as C. rusticus the 
 antennal scale is sometimes no longer than the rostrum ; so that 
 feature is also useless as a means of classification. 
 
 Since in the eighty-five individuals which I have before me 
 not a single character that would separate them into C. rusticus 
 and C. neglectus is found to hold throughout, we must conclude 
 that they are all variations within one species. If I had only 
 the extremes to judge from, I should not hesitate to separate 
 them into two species. However, the general contour of the 
 
 (30) 
 
body and the general form of the first pair of abdominal appen- 
 dages of the male remains constant throughout the series. 
 This, together with the fact that all of these varying gradations 
 are found among individuals that have spent their lives in the 
 same stream, and when they were collected were captured at 
 the same time, seems to indicate that whatever these variations 
 may lead to in the future, they should now all be included under 
 one species. 
 
 That these variations form a graded series in which there 
 is no definite dividing line, I have attempted to show by means 
 of the photographs reproduced in Plate VI. 
 
 These photographs show a series of the differences in form 
 of chelae, rostra and general body contour typical of the col- 
 lection. It is evident that in a series such as this it is not per- 
 missible to say that a certain number of these individuals should 
 be classed as one species and the rest as another. 
 
 Plate VI., Fig. I is one of the specimens which Faxon 
 classified as C. neglectus. According to the same classification, 
 Figs. 2, 8, 9, ii, 12 and 13 would also be called C. neglectus. 
 Figs. 3, 4, 5, 6, 7 and 10 would be classed as C. rusticus. Figs. 
 4, 9, 12 and 13 are females ; the remaining specimens are males. 
 
 In looking over the figures shown in Plate VI. no one will 
 deny that there are some differences which at first sight may 
 appear conspicuous, but these differences are not characteristic. 
 We look at the crayfish called C. neglectus, and decide that a 
 certain form of chela is characteristic; but on the crayfish 
 classed as C. rusticus we find the same sort of chela. If any 
 other character be selected we find the same difficulty. Not a 
 single individual can be found that exactly accords with the 
 description of either species. 
 
 Since this is the case, and since C. rusticus is an old species, 
 it having been nearly half a century since Girard named it, I 
 have, as was mentioned above, classified the whole series under 
 C. rusticus. The species C. medius, which I shall take up next, 
 seems to me to belong under C. rusticus also. 
 
 Cambarus medius, Faxon. 
 
 C. medius has been reported only from Missouri, and from 
 but one locality, Irondale. The only specimens which are 
 known to have been collected are the two from which Faxon 
 named this species. The likenesses and differences between 
 this species and C. rusticus have already been mentioned in dis- 
 cussing C. rusticus. As has been shown, the differences which 
 
 (31) 
 
separate the three species, C. rusticus, C. neglectus, and C. medius, 
 are very slight and inconstant. Knowing, as I do, the vari- 
 ability of the individuals within the species C. rusticus, and con- 
 sidering the fact that Faxon had but two specimens from which 
 to name the species C. medius, it seems to me quite probable 
 that those individuals which Faxon calls C. medius are variations 
 of C. rusticus; and I think that he would have recognized them 
 as such if he had been able to examine a number of individuals. 
 
 I think that a careful comparison of the descriptions of 
 these three species, together with an examination of the varia- 
 tion within the one species C. rusticus, proves that not a single 
 feature which would distinguish one species from another holds 
 through a single series of specimens taken at the same time and 
 place. If one character — e. g., relative lengths of abdomen and 
 cephalotborax — tells in favor of identifying the specimen as 
 C. rusticus, some other character — e. g., length of first pair of 
 abdominal appendages — answers to the description of C. medius. 
 In not a single individual that I have examined have the main 
 distinguishing characteristics between these three species been 
 united. It is clear that such extremely variable characters have 
 not the value of specific characters. 
 
 Within the species of which I have had abundant material 
 to examine (C. virilis), there are greater and more numerous 
 variations among individuals coming from the same pond than 
 are used to separate the three species, C. rusticus, C. neglectus 
 and C. medius. 
 
 Cambarus virilis, Hagen. 
 
 Plates I. and II. 
 
 For synonomy see Faxon (loc. cit. p. 96). 
 
 C. virilis is the most common species in the state. It is 
 found in great numbers wherever it occurs, and it is widely dis- 
 tributed. It has been collected from the following localities in 
 Missouri : St. Louis, Osage River, Irondale ; Washington, 
 Franklin County; Kansas City; Niangua River, Camden 
 County; Marmaduke, Lawrence County; Linn Creek and 
 Columbia, Boone County. Most of the above named places are 
 situated in the central and southern part of .the state. 
 
 C. virilis is especially plentiful in the ponds and streams 
 about Columbia. Upon one occasion in June, 1896, Dr. Ayers 
 collected in the course of two and a half Jiours more than five 
 hundred crayfish of this species. There is one lot in our present 
 
 (32) 
 
collection which contains over twelve hundred individuals. The 
 whole collection of C. virilis contains over three thousand speci- 
 mens. In general the number of females collected exceeds the 
 number of males ; although in one or two lots in the collection 
 the males are in excess of the females. In one lot, taken at 
 Columbia in 1897, there are 162 males and 203 females. Among 
 212 crayfish collected during April, 1899, 80 were males and 132 
 were females. In most collections the males and females are 
 in about the above proportions. 
 
 The abundance of C. virilis renders it an excellent subject 
 for the study of variations within a species, and for a comparison 
 of the differences between the first- and second-form males. 
 
 A special discussion of second-form males will be taken up 
 later. Here it may be mentioned that, besides the difference 
 in the form of the first pair of abdominal appendages, which 
 separates the males into first and second forms, there are other 
 noticeable differences between the two forms. Especially 
 noticeable is the difference in the relative size of the chelse. The 
 9ij} jo uosu^duioo y *ozis 9ui^s 9q; jo spnpiAiput uuoj-;sjij 
 chelse of the second-form individuals are much smaller than in 
 Figs. K and L of Plate I. shows this difference. Fig. K is full 
 and broad, and with outer margin of hand considerably curved. 
 The spines and tubercles are well developed. In Fig. L the 
 hand is thinner and narrower, and the outer margin is nearly 
 straight. The spines and tubercles are less developed than in 
 Fig. K. The crayfish from which Fig. K is taken was 67 mm. 
 long, and the one from which Fig. L is taken was 68 mm. long. 
 
 A still more remarkable difference is seen between Figs. N 
 and O of Plate II. The crayfish, from wnich the former is taken 
 was 74 mm. long, and the one from which the latter is taken 
 78 mm. long. There was no great difference in the size of the 
 two animals, but a very marked disparity existed in the size of 
 the two chelae. The figures are life-size in all cases. For 
 Fig. N the measurements of the hand are: length, 23 mm.; 
 breadth, 9 mm. For Fig. O : length of hand, 39 mm. ; breadth, 
 14 mm. These two chelae also show a more marked difference 
 in the development of the spines than Figs. K and L. 
 
 Immature C. virilis: Even in very young individuals 
 and chelae. 
 
 C. virilis presents a number of variations. The variations here, 
 as in older specimens, are to be noticed mainly in the rostra 
 
 As is well known, the newly hatched crayfish is in some 
 particulars very different from the adult individual, and it will 
 
 (33) 
 
be necessary to speak of some of these differences first. 
 
 When the little animal first comes from the egg the cephalo- 
 thorax is very large in proportion to the abdomen. The abdo- 
 men, thoracic legs and the antennae are flexed under the almost 
 spherical cephalothorax. The different parts of the cephalo- 
 thorax can not at this time be distinguished. The rostrum is 
 very short and bent down between the eyes ; the chelae present 
 very little of the appearance of the chelae of the adult. The 
 beginning of the suture which is to form the joint of the movable 
 finger is only visible under considerable magnification; the 
 tips of the chelae are furnished with recurved hooks ; this is 
 also true of the other chelate appendages, but their hooks are 
 not so strongly recurved as in the chelae. 
 
 With a magnification of one hundred diameters small spines 
 and setae are visible on various parts of the exoskeleton. 
 
 No appendages are present on the first and sixth abdominal 
 somites ; however, the appendages of the sixth somite are 
 already formed and inclosed beneath the telson, from which 
 they are set free after the animal moults. 
 
 The crayfish when first released from the egg is quite help- 
 less, and it remains attached to the swimmerets of the mother 
 for some time. The muscles are still in an embryonic condition. 
 
 Within five or six days a considerable development has 
 taken place, although no moult has intervened. The animal 
 is able to swim about ; the relative size of the cephalothorax 
 is not nearly so great. The remnant of food yolk which was 
 stored up in the cephalothorax has diminished considerably, 
 and now, instead of forming a continuous mass, has separated 
 into two masses, one on either side of the median line, with a 
 clear space between. The cervical groove and areola area can 
 now be distinguished. The spines and setae are much better 
 developed than when the crayfish came from the egg. 
 
 In about nine days after hatching the first ecdysis occurs. 
 At this time the telson fins are set free, and the spines and setae 
 show a marked increase in size. The rostrum is much length- 
 ened, and is no longer bent downward between the eyes ; small 
 rostral spines have made their appearance. The chelae have 
 lost their recurved hooks. The abdomen and cephalothorax 
 have assumed about the same relative proportions as are found 
 in the adult. The appendages of the first abdominal somite 
 have not yet appeared, although a minute swelling under the 
 skin can be seen, and the appendages wilt be set free after the 
 
 (34) 
 
next moult. The animal at this stage measures 7 to 8 mm. I 
 have seen these appendages on C. gracilis 15 mm. long. The 
 appendages had evidently just appeared, for previous to this 
 they were simple little buds, without any differentiation into 
 segments. At 18 mm. there is a separation into protopodite 
 and distal portion of the appendage, but no division indicating 
 a separation into endopodite and exopodite. Whether these 
 appendages appear earlier or later in C. virilis, I do< not know, 
 having had no specimens of this species to examine ; but I think 
 it probable that C. virilis would be somewhat larger, since the 
 adults in C. virilis are of somewhat greater size than C. gracilis. 
 
 After the first moult the young crayfish do not yet leave the 
 protection of the mother, but either attach themselves to or 
 detach themselves from the swimmerets of the female, as suits 
 the occasion. 
 
 A small part of the food yolk still remains, but in four or 
 five days after the ecdysis it has all disappeared, and the little 
 animal must then shift for itself. 
 
 At this stage the young crayfish are almost transparent, 
 and by placing a live one under the microscope the circulation 
 of the blood in the gills, the beating of the heart and the passage 
 of the water through the gill chambers may be observed. From 
 the ventral side, can be seen the double nature of the nerve cord 
 through the length of the abdomen and a part of the cephalo- 
 thorax. 
 
 The areola is relatively broader in the young crayfish than 
 in the adult. A crayfish about nine days old, 8 mm. long, has 
 an areola .3 mm, wide ; that is, the breadth of the areola is to 
 the length of the animal as 1 to 27 ; a crayfish 68 mm. long has 
 an areola about 1 mm. wide ; thus the relative length of body 
 and areola is as 1 to 68 in the adult. 
 
 The gill system of the newly hatched crayfish appears to 
 be identical with that of the adult. I have examined a number 
 of crayfish just from the egg, and in no case have I been able 
 to discover any trace of a gill on the last thoracic somite. 
 
 I was enabled to make these observations on the very 
 young by taking females in berry and hatching the eggs in the 
 laboratory; thus far I have succeeded in studying them from 
 the time of hatching through the first moult. 
 
 At this very young stage but little variation can be noted. 
 By the time they are 9 or 10 mm. long, variations are conspicu- 
 ous. One of the most noticeable points of difference at this 
 stage is seen in the length and shape of the rostrum. Some of 
 
 (35) 
 
them show rostral spines by the time they are 10 mm. long, 
 others show no signs of these spines ; but then we often find 
 mature C. virilis devoid of rostral spines, and it may be that the 
 adult individuals, instead of having lost these spines in the 
 course of development, have never possessed them. 
 
 At 9 or 10 mm. the chelae show nothing particularly char- 
 acteristic of C. virilis, but variations in the relative proportions 
 of the appendages are already present. 
 
 By the time the young animal is 18 mm. long, the chelae 
 show a characteristic which is one of the most constant of the 
 species, namely, the smooth, thickened margin on the outer 
 contour of the hand. This margin is always present in a regen- 
 erated claw; after the first moult, and so far as my experience 
 with the species goes, it is the only characteristic that may be 
 considered absolutely constant. 
 
 There is some variation in relative lengths of abdomen and 
 cephalothorax. The following is a table of measurements 
 taken from individuals varying from 35 to 45 mm. in length: 
 
 LENGTH OF BODY 
 
 LENGTH OF 
 ABDOMEN 
 
 LENGTH OF 
 CEPHALOTHORAX 
 
 35.00 mm. 
 
 20.10 
 
 mm. 
 
 15.00 
 
 mm. 
 
 44.00 " 
 
 24.00 
 
 a 
 
 20.00 
 
 (< 
 
 44.00 " 
 
 23.00 
 
 i i 
 
 21.00 
 
 i t 
 
 40.00 " 
 
 21.50 
 
 a 
 
 18.50 
 
 a 
 
 35.00 " 
 
 18.50 
 
 a 
 
 16.50 
 
 1 1 
 
 44.00 " 
 
 24.00 
 
 it 
 
 20.00 
 
 a 
 
 43.00 " 
 
 23.00 
 
 a 
 
 20.00 
 
 a 
 
 44.00 " 
 
 22.50 
 
 a 
 
 21.50 
 
 a 
 
 42.00 " 
 
 22.00 
 
 it 
 
 20.00 
 
 1 1 
 
 42.00 " 
 
 22.00 
 
 a 
 
 20.00 
 
 a 
 
 It is to be noticed that these variations are not so marked 
 as those found in C. gracilis, although in other respects 
 C. gracilis is by far the more constant species. In C. virilis the 
 abdomen is in every case longer than the cephalothorax. 
 
 Much greater variation is found among adults of C. virilis 
 than among the young; even though they have been collected 
 in the same vicinity, out of the same pond of creek. 
 
 Following are the descriptions of a number of figures which 
 show the variations in rostra, chelae and first pair of abdominal 
 appendages of the male. 
 
 (36) 
 
Plate I., Fig. A shows the chelae, rostrum and first pair of 
 abdominal appendages of a first-form male 106 mm. in length, 
 taken at Columbia. The hand is long, thin and very spinous, 
 and with outer contour very much curved. The carpus has two 
 well-defined spines on the median border. The meros two 
 spines on its upper border. The rostrum is long and narrow, 
 with the rostral spines almost obsolete. The abdominal 
 appendages have three well defined tufts of setae arranged along 
 their inner borders. The tufts of setae on the lower projection 
 is very unusual. 
 
 Plate I., Fig. B shows chela, rostrum and first pair of 
 abdominal appendages of a first-form male 80 mm. long. This 
 individual was also taken at Columbia. The general outline of 
 the hand is much the same as in Fig. A, but the spines are not 
 so well developed and the hand is not so thin. There are three 
 instead of two spines on the upper border of the meros. The 
 rostrum is especially noticeable on account of its many angles. 
 This form of rostrum is not common. The abdominal append- 
 ages have only two tufts of setae, and are not so much curved 
 as in Fig. A. 
 
 Plate I., Fig. C shows chela, rostrum and first pair of 
 abdominal appendages of a first-form male 71 mm. long, col- 
 lected at Columbia, 1895. This shows a hand relatively much 
 shorter and thicker than the previous specimens. The spines 
 are much less developed than in Figs. A and B ; the distribution 
 is about the same, except that on the meros there is but one 
 spine, and that, one small. The rostrum is short and broad, 
 with an obtuse apex and no spines. The abdominal appendages 
 are thicker compared with their length than in the preceding 
 specimens. 
 
 Plate I., Fig. D shows chela, rostrum and first pair of 
 abdominal appendages of a first-form male 82 mm. in length, 
 taken at Columbia, 1895. The hand is long and thin, the spines 
 small and the movable finger crooked. The carpus has three 
 spines on its inner border, and the meros has but one on its 
 upper border. The rostrum is of medium length, the sides 
 almost parallel and the acumen acutely angular. The abdomi- 
 nal appendages are relatively long and slender, and show but 
 one well developed tuft of setae. 
 
 Plate I., Fig. E shows chela, rostrum and first pair of 
 abdominal appendages of first-form male 91 mm. in length. 
 The hand is long and thin, the opposable edges of the fingers 
 
 (37) 
 
bordered by large, blunted spines. On the median border of 
 the carpus is a very large spine and one small one; on the 
 upper surface is a group of three small spines. The meros has 
 two spines on its upper surface. The rostrum is long and 
 narrow, with convex apex, and entirely destitute of rostral 
 spines. The abdominal appendages are long, slender, and less 
 curved than in some individuals ; they show two tufts of setae, 
 one on the lower median projection, which is not at all common 
 in any species with which I am familiar. 
 
 Plate L, Fig. F shows rostrum and first pair of abdominal 
 appendages of a second-form male 102 mm. long, taken at 
 Columbia in the same collection as Figs. C, D and E. No 
 normal chelae were present, which is the usual state of affairs 
 in a large second-form male. The rostrum is long, with sides 
 slightly concave, and. with the base very little broader than the 
 distal end ; sides of the apex also concave, acumen sharp- 
 pointed, with small median carina. The abdominal appendages 
 are long, slender and considerably curved. 
 
 Plate I., Fig. G shows rostrum and first pair of abdominal 
 appendages of a second-form male 98 mm. long. This is also 
 from the same collection as Fig. F, being short, almost tri- 
 angular, with a very broad base, and with an extremely acute 
 acumen, and with conspicuous rostral spines. The abdominal 
 appendages are not so strongly curved or so slender as in 
 Fig. F. 
 
 Plate L, Fig. H shows chela, rostrum and first pair of 
 abdominal appendages of a first-form male 98 mm. in length, 
 belonging to the same collection as the preceding figures. The 
 hand has a strongly curved external margin, and the inner 
 margin of the fingers are widely gaping and bordered by well 
 developed, blunted spines. The carpus is furnished with two 
 sharp spines on its median border. The meros has but one 
 spine on its upper surface. The rostrum is triangular, of 
 medium length, and has a very sharp apex. The abdominal 
 appendages are long, much curved, and show two tufts of setae 
 on median borders. 
 
 With the exception of the first two above described figures 
 (Figs. A and B), all of the individuals from which these figures 
 were drawn were collected in the same vicinity during the same 
 year. The specimens from which Figs. A and B were drawn 
 were collected in the same vicinity, but not during the same 
 year. These crayfish had passed their lives under practically 
 identical conditions, and yet present marked variations. Still 
 
 (38) 
 
each individual presents enough of the characteristics of the 
 species to make it certain that they all belong to the same 
 species, wide apart as the extremes are, for there is a closely 
 graded series of intermediate stages. Crayfish from different 
 localities within the same state also show variations, but not 
 more marked than those which are to be seen among individuals 
 of the same locality. 
 
 I have had no opportunity to examine an extensive series 
 of the same species coming from different states ; but it seems 
 reasonable to suppose that these might show variations different 
 from those among individuals of practically the same locality. 
 
 Following is a further description of the variations of 
 C. virilis, all of which were taken in Missouri. 
 
 Plate I., Fig. I shows chela, rostrum and first pair of 
 abdominal appendages of a second-form male 74 mm. long, 
 taken November, 1898, at Columbia. The hand is small and 
 the spines adorning it are small; both are relatively much 
 smaller than the hand and spines of a first-form male of the 
 same size. The rostrum is long, with parallel sides, a very 
 sharp acumen and no lateral spines. The abdominal appendages 
 are slender and straight, with curved tips. 
 
 Plate I., Fig. J shows chela, rostrum and first pair of 
 abdominal appendages of a first-form male 62 mm. in length, 
 taken at Columbia, November, 1898. Hand is relatively much 
 thicker than that of the second-form male shown in the pre- 
 ceding figure; the spines are also much better developed. 
 Movable finger is considerably curved; carpus with one very 
 prominent spine and two smaller ones ; meros with two sharp 
 spines on upper surface. Rostrum triangular, with sharp- 
 pointed acumen. Abdominal appendages with a gradual curve 
 throughout their whole length. 
 
 Plate I., Fig. K shows chela, rostrum and first pair of 
 abdominal appendages of first-form male 6j mm. long, taken 
 at Columbia. External border of the hand strongly curved, 
 spines small. Carpus with two well developed spines on median 
 border; a row of small tubercles on the upper surface. Two 
 small spines on the upper surface of meros. Abdominal append- 
 ages more slender and less curved than in Fig. J. 
 
 Plate II., Fig. L shows chela, rostrum and first pair of 
 abdominal appendages of second-form male 68 mm. in length, 
 taken at Columbia. Hand small and their spines small. Carpus 
 with one large and two small spines on internal border. Meros 
 with two inconspicuous spines on its upper surface. Rostrum 
 
 (39) 
 
long, with parallel sides and very sharp acumen. Abdominal 
 appendages slender and straight, except at the tips. 
 
 Plate II., Fig. M shows chela, rostrum and first pair of 
 abdominal appendages of a first-form male in mm. in length, 
 taken at Columbia, March, 1897. This figure should be com- 
 pared with Plate I., Fig. A, for both crayfish were taken from 
 the same pond at the same time. The hand is very large and 
 thick, with a much curved external border; opposable edges 
 of the fingers bordered with large, blunted tubercles. Carpus 
 with one long and two short spines on median border, and with 
 small tubercles scattered about on the upper surface. Meros 
 with well developed spines on the upper surface. Rostrum 
 large, with parallel sides, median carina in distal third, rostral 
 spines almost obsolete, acumen sharp and long. Abdominal 
 appendages long and slender, with three tufts of setae. As was 
 mentioned in connection with Fig. A of Plate I., the tufts of 
 setae on the lower median projection is quite unusual in this 
 species. 
 
 Plate II., Fig. N shows chela, rostrum and first pair of 
 abdominal appendages of a second-form male 74 mm. in length, 
 taken in Camden County, March, 1897. Hand very small and 
 straight, with very small spines. Carpus with well developed 
 spine on the median border. Meros with two small spines. 
 Rostrum short, broad, triangular, with obtuse acumen. Abdom- 
 inal appendages straight and slender, setae very inconspicuous. 
 
 Plate II., Fig. O shows chela, rostrum and first pair of 
 abdominal appendages of a first-form male 78 mm. in length. 
 Hand large and thick, with external border much curved, 
 tubercles and spines well developed. Carpus with two well 
 developed spines on median border. Meros with two small 
 spines on upper surface. This chela shows a marked difference 
 from the one shown in Fig. N of Plate II. ; although there is 
 very little difference in the size of the crayfish from which the 
 two were taken ; and it should be added that the two individuals 
 were found at the same time and place. The rostra in Figs. N 
 and O are very similar. The abdominal appendages are much 
 alike, except that those shown in Fig. O are much more curved 
 than those shown in Fig. N. 
 
 Plate II., Fig. P shows chela, rostrum and first pair of 
 abdominal appendages of a first-form male no mm. long, taken 
 at Mt. Vernon, Lawrence County, April, 1897. Hand very long 
 and thin, with small spines, outer margin straight and upper 
 surface flat. Carpus with two well developed spines on median 
 
 (40) 
 
border. Meros with two small spines on upper surface. It is 
 probable that this chela is a regenerated one, for I have seen 
 this same form of chela on one side of the body, while on the 
 other side the chela was large and thick, but on the specimen 
 from which this figure is taken both chelae were of the same 
 character and of about equal size. There were also several 
 other individuals of the same collection which had chelae like 
 these. The difference is so very marked that one would, unless 
 he had thick-clawed individuals at hand, be tempted to classify 
 the thin-clawed ones as something other than C. virilis. Ros- 
 trum broad, with almost parallel sides, and with obtuse acumen. 
 Abdominal appendages long and slender, without conspicuous 
 setae. 
 
 Plate II. , Fig. Q shows chela, rostrum and first pair of 
 abdominal appendages of a first-form male 1 10 mm. long, taken 
 at the same time and place as that of Fig. P, Plate II. Hand 
 very large and thick, with much curved external border, spines 
 well developed, opposable surfaces of the fingers bordered by 
 large, blunt tubercles. This hand is markedly different from 
 the hand in Fig. P. Carpus with two sharp spines on internal 
 border. Rostrum shorter and narrower than in Fig. P. 
 Abdominal appendages shorter and not so slender as in the 
 preceding figure. 
 
 Plate II., Fig. R shows chela, rostrum and first pair of 
 abdominal appendages of first-form male 82.5 mm. long, taken 
 at Columbia. Hand short and relatively very thick, movable 
 finger crooked. Carpus with one short spine and one very 
 small one on median border. Meros with three spines on 
 upper surface. Rostrum with concave edge and sharp acumen. 
 Abdominal appendages relatively thick, slightly curved, and 
 with two tufts of setae. 
 
 It will be noticed that all the above described variations 
 have been found among individuals within this state and in 
 only three different localities. Individuals from other localities 
 might also have been chosen, but from these three I was enabled 
 to select all the representative variations that are shown in the 
 collection. 
 
 FIRST AND SECOND FORMS. 
 
 Since the publication of Hagen's " Monograph of the North 
 American Astacidae," we have known of the existence within 
 each species of Cambarus of two distinct forms or varieties of 
 the males. This variation finds expression in the shape of the 
 
 (41) 
 
first pair of abdominal appendages. In consequence of this the 
 males are usually designated as first- and second-lorm males. 
 
 The first pair of abdominal appendages in the second form 
 are similar to the same pair of appendages in the young, imma- 
 ture males. In the first-form males these appendages have the 
 distal terminations much more slender, and often fine pointed 
 instead of blunt, as is always the case with the distal terminations 
 in the second form. 
 
 The fact that the second-form appendages have the same 
 general form as the appendages of the immature males led to 
 the supposition that the second-form males are sterile. Faxon 
 states that the testes are smaller and the vasa deferentia shorter 
 in the second form than in the first. He also suggests that 
 these two forms are alternating conditions in the life of the same 
 individual, the first form being acquired during the breeding 
 season and the second form during the other seasons. These 
 changes, of course, can not take place without intervening 
 moults, but Faxon really observed that some crayfish which 
 he had in a tank moulted from first-form into second-form. 
 However, he did not carry his observations far enough to 
 determine when, if ever, they again reverted to the first form. 
 Neither has he offered any explanation as to a probable cause 
 of the change from one form to the other. 
 
 The fact that a first-form male will moult into a second- 
 form precludes the idea that the second form in any true sense 
 represents a developmental stage in the individual. Also the 
 fact that we often find in C. virilis and C. rusticus at least small 
 first-form males 40-45 mm. long, living side by side with second- 
 form males 80-100 mm. long, shows that the size of the indi- 
 vidual bears no relation to the condition of first or second form. 
 Hence an explanation must be sought elsewhere. 
 
 During the past two years, in the course of my taxonomic 
 studies, I have had occasion to examine a great many males of 
 each form, especially of the species C. virilis. This abundance 
 of material has given me an opportunity to make very complete 
 observations on the two forms. 
 
 In looking over alcoholic specimens, I noticed that when- 
 ever I found a large second-form male, 80-95 mm - l° n g> tnat 
 it never had perfect, well developed chelae. There were either 
 no chelae, or the chelae present were in a very imperfect state 
 as regards size and sculpture, indicating that they had been lost 
 and were now being regenerated. Finding this uniformly the 
 case, I was led to surmise that the existence of first and second 
 
 (42) 
 
forms is connected with the presence or absence of chelse. It 
 will be remembered that the chelse of the second-form males 
 are always described as smaller and with smaller spines and 
 tubercles than those of first-form males of a corresponding size. 
 
 On April 22, 1899, I to °k a number of large first-form 
 males and broke off both chelae, expecting them soon to moult 
 into second-form individuals. In this I was not disappointed, 
 for during the next two or three weeks several of them moulted, 
 each one into a second form. However, I noticed a difference 
 between the second-form with chelae and the second-form with- 
 out chelae. The first pair of abdominal appendages of those 
 with chelae are not so slender; they are as individuals without 
 chelae. The basal half of the appendage has the usual shape of 
 the first-form appendages, and although the rami are blunt, as 
 is usual with the second-form, they are not so closely approxi- 
 mated, and the tip of the inner ramus is more dilated than in 
 the second form without chelae. (Plate IV., Figs. A and C.) 
 The appendages shown in Fig. A are from a second-form male 
 without chelae, and the appendages shown in Fig. C are from 
 a second-form male with chelae. 
 
 When it was found that the crayfish, whether with or with- 
 out chelae, and whether first- or second-form, all moulted into 
 second-form, it became evident if there were to be first-form 
 males the next year, there must be a second moulting season 
 during the summer. For in every case that I have been able 
 to observe, a male that is already second-form in the spring, 
 moults again into second-form. But, as I stated above, these 
 are individuals that have no chelae at all, or only imperfect ones. 
 
 That there are really two moulting seasons I had already 
 suspected ; for while engaged in doing some experimental work 
 upon crayfish, I found that usually the animal moulted in April 
 or May, and again between the first of June and the last of 
 August. However, I was not sure that mutilation did not 
 increase the frequency of the moults. But my observations 
 between May first and the middle of July, 1899, proved that nor- 
 mally each male crayfish moults at least twice a year. The time 
 from March to November will include both moulting seasons 
 for C. virilis. 
 
 The first moulting season begins in April, and by the middle 
 of May very few crayfish can be found that have not recently 
 moulted. During the first moulting season all the males moult 
 into second-form. However, all the males with large chelae 
 have the bases of the first pair of abdominal appendages meet- 
 
 (43) 
 
ing in the median line, while those males with small chelae, or 
 with no chelae, do not have these appendages meeting in the 
 median line. (Plate IV., Figs. B and F.) The difference in 
 shape and development of the bases, and in the general sculp- 
 ture of the appendages, is noticeable in Figs. B and F. In 
 Fig. F the appendage has much more of the general appearance 
 of a first-form appendage than in Fig. B. 
 
 The fact that all males moult into second-form during the 
 first moulting season accounts for the great number of second- 
 form individuals that are taken at some seasons, while compara- 
 tively few are taken at other times. Males from collections 
 made in May are likely to be mostly second-form. But collec- 
 tions made after the first of July will contain a relatively small 
 number of second-form males. We have one collection made 
 in early June that contains over seven hundred and fifty second- 
 form males and only five first-form. In the collections made 
 in the spring of 1899, before May first, not more than six or 
 seven second-form males were taken, and they were all of 
 medium size. From the tenth of May to the tenth of June the 
 collections contained very few first-form males. 
 
 By the tenth of June the second moulting season is well 
 begun, and by the first of July comparatively few second-form 
 males are to be found. Although now and then on through 
 July and August a moulting specimen may be found. 
 
 Having found that all the males, whether large or small, 
 moulted into the second form during the first moulting season 
 of the spring, I expected to find that at the second moult the 
 males with chelae would again be transformed into first form, 
 while those without chelae would retain the second-form append- 
 ages after the second moult. That such is really what happens, 
 my observations have verified; in every instance males pos- 
 sessed of two or even one well developed chela, have at the 
 second moulting returned to the first form, and those without 
 chelae have retained the second-form appendages after the 
 second moult. 
 
 This appears to be conclusive evidence that the relation 
 between the chelae and first pair of abdominal appendages is 
 such a close one that the loss of chelae will produce a change 
 in the form of the sexual appendages which is more or less 
 permanent. In other words, a first-form male that loses its 
 chelae before or at the time of the first moult, will at the second 
 moult still retain the second-form appendages ; a crayfish that 
 loses its chelae after the first moulting season of any given year, 
 
 (44) 
 
but. before the second moulting season, may or may not moult 
 into the second-form again at the second moult, depending upon 
 how near the second moult is at hand when the chelae are broken 
 off. A male having once lost its chelae will continue to moult 
 as second-form until the new chelae have attained a considerable 
 size. 
 
 In a collection of crayfish brought into the laboratory this 
 spring, May 10, 1900, I found one about 7 J mm. long that had 
 recently moulted into second-form, and with both chelae missing. 
 The stumps of the chelae were quite smooth, and no signs of 
 the regeneration of these appendages had yet appeared. Quite 
 likely the chelae had been lost during the last moult, which had 
 evidently taken place only a few days before. May 13th, three 
 days after I had found this crayfish, it again moulted into 
 second form. At this moult there was only the rudiment of 
 a new chela. A minute bud had appeared, which showed no 
 semblance whatever to an appendage. Then on June 17th this 
 crayfish moulted for the third time, still retaining the second- 
 form appendages. Between the last two moults, May 13th to 
 June 17th, the chelae had grown to such an extent that when they 
 were released from the confining skin at the third moult, they 
 expanded to more than an inch in length. 
 
 August 10th this crayfish died without having moulted 
 again. At the time it died the chelae measured 36 mm. in length 
 and 5 mm. in width, this entire growth having been made in 
 three months. 
 
 Judging from the small, imperfectly developed chelae which 
 I have seen on the other second-form individuals, I think it 
 scarcely probable that, had this crayfish lived through another 
 moult, it would have then reverted to first-form, for the chelae 
 would still not have been so large as it appears requisite for 
 them to be in order that the crayfish be first-form. For it is 
 well known that the growth of the chelae is quite slow after the 
 moult in which the chelae first appear in the form of true jointed 
 appendages. Plate IV., Fig. K, shows the chelae, natural size, 
 of the crayfish described above. Although this growth took 
 place within three months, most of it occurred between 
 May 13th and June 17th, very little over a month. The chelae 
 were only 36 mm. long when the crayfish died, August 10th; 
 they were fully 33 mm. long June 17th. Only a minute bud had 
 appeared between May 13th and June 17th, and only 3 mm. 
 between June 17th and August 10th, an interval almost twice as 
 long. 
 
 (45) 
 
From the above consideration it is readily seen, on the 
 hypothesis that absence of chelae is the cause of a crayfish 
 remaining second-form through two or more successive moults, 
 that it is altogether possible that a crayfish remains second-form 
 through several moults — e. g., four or five at least. We have 
 positive evidence that they can and do remain second-form 
 through three successive moults when the chelae have been 
 broken off, and that when chelae are present, the crayfish alter- 
 nate from first-form to second-form with each moult. 
 
 I might here add that C. gracilis furnished some negative 
 proof that loss of chelae perpetuates second-form males. Faxon 
 states that second-form individuals among C. gracilis are 
 unknown. There are two facts to be noticed which help to 
 explain this absence of the second-form in this species. First, 
 as I have mentioned in discussing the species, their moulting 
 season has never been discovered, and there are, at most, only 
 a limited number of males in any collection. Of course, the 
 fact that the time of moulting is unknown does not explain 
 why the second-form has not accidentally been found instead 
 of always first-form. But the extreme scarcity of the males 
 may help to explain this. 
 
 The second fact to be noticed in this connection is that 
 C. gracilis never shows that there has been a loss of parts, as 
 chelae or other appendages. When individual C. gracilis are 
 first captured, no appendages are broken except those which 
 show evidences of having been broken in capturing them. Now 
 the only grounds upon which I attempt to explain this are, that 
 the external conditions to which the animals are subjected are 
 such as favor a minimum of accidents. Living in their burrows 
 as they do, it seems that they are able to avoid many misfor- 
 tunes which come upon other species of crayfish that habitually 
 live in the streams and ponds. In none of the collections of 
 C. gracilis which I have seen has there been an individual with 
 a broken chela, unless there was evidence that it had been 
 recently broken. Since none have moulted in my laboratory, 
 of course there is no way of determining whether they moult 
 into second-form or not, or whether breaking off the chelae 
 would cause them to moult into second-form. From what we 
 known of other species of Cambarus, it is fair to suppose that 
 males of C. gracilis normally have two moulting seasons ; at the 
 first, moulting into second-form, and at the second returning 
 to first form. 
 
 Experiments have proven that young C. gracilis repair an 
 
 (46) 
 
injury and regenerate a lost or broken appendage as readily as 
 the young of any other species. And though they are seldom 
 injured, they seem not to have lost in the least the power of 
 regenerating lost parts. My observations and experiments on 
 this species have been confined to young specimens, 35 or 
 40 mm. in length. 
 
 It is not unusual to find first-form males without chelse, but 
 either only bare stumps are present, or the new growth that 
 has occurred shows that no moult has taken place since the 
 chelse were broken off. It is quite probable that the chelse were 
 broken off during the last moult; for it often happens that a 
 crayfish loses one or more appendages in his efforts to free 
 himself from his old shell. 
 
 The loss of but one chela does not seem to sufficiently 
 derange the mechanism of the animal to change it from first to 
 second form. However, in a number of instances I have found 
 indications that the loss of one chela affects the reproductive 
 organs. 
 
 During March and early April, in making some dissections, 
 I noticed in two instances where one chela was missing; that 
 on the opposite side of the animal the vas deferens was much 
 shorter than on the side from which the chela was gone. 
 Having noticed this difference in two instances, I dissected a 
 number of other crayfish with but one chela, and in every case 
 where it was evident that the chela had been lost for some time 
 I found this same difference between the reproductive organs 
 of the two sides. The shortening of the vas deferens was always 
 on the opposite side from the missing chela, irrespective as to 
 whether it was the right or left chela. 
 
 For comparison I examined a number of other males 
 having both chelse present. Without exception I found the vasa 
 deferentia equally developed on each side. Had I found this 
 difference between the vasa deferentia of males with two chelse 
 and males with one chela to remain constant for all seasons of 
 the year, I should have considered it positive proof that the loss 
 of the chelse is directly connected with the degeneration of the 
 reproductive organs. Although I found this to be true for 
 every case examined during the latter part of March and early 
 April, in June, when I came to examine males with but one 
 chela, this difference was no longer apparent. I can offer no 
 explanations for these facts as yet. 
 
 It is well known that the reproductive organs vary consid- 
 erably in size and development at different seasons of the year, 
 
 (47) 
 
being larger and better developed during late summer and early 
 autumn, just before and at the time of the breeding season than 
 at other times of the year. There is also known to be a differ- 
 ence in the relative development of the testes and vasa deferentia 
 of the first- and second-form males, but this difference is much 
 more conspicuous during some seasons of the year than others. 
 
 During the last few days of March, 1899, and the first two 
 weeks of April, I examined the reproductive organs of both first- 
 and second-form males. This was done before the first moult- 
 ing season began. For comparison I took them in pairs, a 
 first-form and a second-form of the same size. In each instance 
 I found a marked difference between the reproductive organs of 
 the two, especially of the vasa deferentia. In the first-form the 
 vasa deferentia were always much convoluted, while in the 
 second-form these organs were usually straight, having at most 
 not more than one or two convolutions. 
 
 About the first of May I again examined a number of cray- 
 fish that had passed through the first moulting season. Then, 
 as before, I found that males having the first pair of abdominal 
 appendages thick, with rami gaping and tip of inner ramus 
 dilated, indicating that the animal was of the form that would 
 moult into the first-form at next moult, invariably had much 
 convoluted and well developed vasa deferentia. Males whose 
 first pair of abdominal appendages were slender, indicating that 
 they were of true second-form, had in every case unconvoluted 
 vasa deferentia. 
 
 In early June, after the beginning of the second moulting 
 season, I again examined first-form and second-form males. 
 Although I found that the shape and size of the testes and the 
 convolutions of the vasa deferentia of different individuals varied 
 considerably, I did not find, as I had previously, that the repro- 
 ductive organs of the second-form males were much less devel- 
 oped than those of the first-form males. (Plate IV., Figs. D 
 and B.) Neither was there any constant difference in the shape 
 of the testes of the first-form and second-form males. 
 
 If it is true, as my first observations seem to indicate, that 
 a loss of the chelae results in a reduction in size of the repro- 
 ductive organs, then a male that loses its chelae at second 
 moult — that is, when it moults from second-form into first- 
 form — should after a time show a degeneration of the repro- 
 ductive organs. Proceeding on this Irypothesis, I took, June 
 27th, a first-form male 90 mm. long, thatiiad lost its chela in 
 the last moult, nearly three weeks before, and for comparison 
 
 (48) 
 
a first-form male of the same size, with the chelae present, and 
 found that the vasa deferentia of the one with chelae were no 
 better developed than those of the one without chelae. How- 
 ever, the testes were larger and better developed. A micro- 
 scopic examination showed that the testes of the one with chelae 
 were filled with spermatazoa in an advanced stage of develop- 
 ment, while the testes of the one without chelae contained very 
 few spermatazoa, and these few were in the early stages. 
 
 The reproductive organs from another pair somewhat 
 larger, otherwise similar, individuals were then examined. So 
 far as size was concerned, there was very little difference in the 
 reproductive organs of the two individuals; but microscopic 
 examination again showed great numbers of spermatazoa in 
 advanced stages in the vasa deferentia and testes of the one 
 with chela, and practically no spermatozoa at all in the vasa 
 deferentia and testes of the one without chelae. 
 
 I then examined the reproductive organs of a first-form 
 male 98 mm. long, that had had the chelae taken off April 22d, 
 about two months before, and had been in the laboratory since 
 that time without moulting. Apparently the testes were much 
 degenerated; they were small and semi-transparent. (Plate 
 IV., Fig. J.) But the vasa deferentia were large and convo- 
 luted ; at the ends near the external openings they were opaque 
 and milky looking. A part of the distal end of a vas deferens 
 was examined, and found to be filled with spermatozoa of 
 advanced stages. 
 
 Whether or not the testes were permanently degenerated 
 could not be decided. Certain it was that at that time they 
 presented an unnatural appearance. The fact that the vasa 
 deferentia were full of spermatozoa does not argue for the active, 
 healthy condition of the testes, for it is well known that in many 
 animals the spermatozoa retain their vitality for long periods, 
 and these spermatozoa which filled the vasa deferentia of this 
 crayfish may have been in the vasa deferentia for a long time. 
 
 Although I consider it a well-established fact that pres- 
 ence or absence of chelae determines whether an individual male 
 crayfish is to be first or second form, yet at the present there 
 appears no way of determining whether the second form is 
 sterile or not. 
 
 SUMMARY. 
 
 1. The examination of thousands of specimens of the spe- 
 cies C. virilis has led to the conclusion that there are greater 
 
 (49) 
 
variations within this one species than are often used to separate 
 individuals into different species, and the variations involve the 
 characters used for classification. 
 
 2. In view of the extremely diverse variations found within 
 the species C. rusticus (Girard), it is desirable to include the 
 recently described species C. neglectus (Faxon) under C. rusticus, 
 since the variations found within this last named species include 
 every characteristic that could be used to separate the two 
 species. 
 
 3. Relative lengths of cephalothorax and abdomen, length 
 of first abdominal appendages of the male, presence or absence 
 of spines, shape of chelae and rostrum, can not be relied upon as 
 specific distinguishing characteristics ; e. g., C. virihs shows 
 almost every shape of rostrum described within the genus 
 Cambarus. 
 
 4. Two new species, C. ayersii, Group I., and C. whitmani, 
 Group IV., are described for the first time. 
 
 My work upon the second-form males has led me to the 
 following conclusions : 
 
 1. Normally, in C. virilis at least, every adult male moults 
 in the spring into second-form. 
 
 2. In the course of six weeks or two months all adult males 
 in possession of normal chelae moult a second time, and revert 
 again to first-form. 
 
 3. Males without chelae or with only imperfect ones also 
 moult a second time during the same season, but still retain 
 the second-form appendages. 
 
 4. Males without chelae or with imperfect ones continue 
 to moult into second-form until the chelae have reached a size 
 normal for the size of the animal. 
 
 5. In late fall and during winter and spring there is a 
 noticeable difference between the reproductive organs of the 
 first-form and second-form males, the testes and vasa deferentia 
 of the second-form males apparently being much less developed 
 than the same organs in the first-form males. 
 
 '6. During the summer, though the reproductive organs 
 of different individuals show great variation, there are no dis- 
 tinguishing characteristics by which the reproductive organs 
 of first-form and second-form males can with certainty be 
 distinguished. 
 
 7. Though there is some evidence in favor of regarding 
 second-form males as sterile, there is as yet no positive proof 
 of it. 
 
 (50) 
 
BIBLIOGRAPHY. 
 
 '84. Abbot, C. C. — Are the Chimneys of Burrowing Crayfish 
 Designed? American Naturalist, Vol. XVIIL, Nov., p. 
 
 1157. 
 
 '85. Abbot, C. C— How the Burrowing Crayfish Works. The 
 Inland Monthly, Vol. I., Feb., pp. 31, 32. 
 
 '44. Audubon. — Birds of America, 8vo. ed., Vol. VI., p. 57. 
 
 'J2. Chrantran, S. — Sur la fecundation des ecrevisses. Compt. 
 Rend., t. 74, pp. 201, 202. Paris. 
 
 '85. Faxon. — Revision of the Astacidae. Part I. Genera of 
 Cambarus and Astacus. 
 
 '89. Faxon. — Notes on North American Crayfishes, Fam. Asta- 
 cidae. Proceedings of the United States Natural Museum, 
 Vol. XII., pp. 625-628. 
 
 '89. Garman. — Cave Animals from Southwestern Missouri. 
 Bulletin of the Museum of Comparative Zoology, at Har- 
 vard College, Vol. XVII., No. 6. 
 
 '95. Herrick. — The American Lobster. Bulletin of U. S. Fish 
 Commission, p. 35, ft'. 
 
 '84. Tarr, R. S. — Habits of Burrowing Crayfish in the United 
 States. Nature, Vol. XXX., June 5th, p. 127. 
 
 EXPLANATION OF PLATES. 
 
 Plates I. and II. 
 
 The figures in Plates I. and II. each show chela, rostrum 
 and first pair of abdominal appendages (male) of individuals of 
 the species C. virilis. In each figure the parts from one indi- 
 vidual are grouped together in the same order. 
 
 Fig. A — Ac, chela; Ar, rostrum; Aa, abdominal append- 
 ages. The letters c, r and a apply to the same parts in each 
 figure on the plates. 
 
 In Plate I., Figs. A, B, C, D, E, H, J and K are taken from 
 first-form males. Figs. F, G, I and L are taken from second- 
 form males. 
 
 In Plates II., Figs. M, O, P, Q and R are taken from first- 
 form males. Fig. N, from a second-form male. 
 
 Plate III. 
 
 Figs. Ai to A5 inclusive show a developmental series of 
 the first pair of abdominal appendages of the male C. gracilis. 
 Fig. Ai, from an individual 23 mm. in length. 
 Fig. A2, from an individual 27 mm. in length. 
 
 (51) 
 
Fig. A3, from an individual 33 mm. in length. 
 
 Fig. A4, from an individual 40 mm. in length. 
 
 Fig. A5, from an individual 67 mm. in length. 
 
 Figs. Bi to B8 inclusive show a developmental series of 
 the annulus ventralis of the female C. gracilis. 
 
 Fig. Bi, from an individual 20 mm. in length. 
 
 Fig. B2, from an individual 23 mm. in length. 
 
 Fig. B3, from an individual 27.5 mm. in length. 
 
 Fig. B4, from an individual 30 mm. in length. 
 
 Fig. B5, from an individual 35 mm. in length. 
 
 Fig. B6, from an individual 36 mm. in length, 
 
 Fig. B7, from an individual 50 mm. in length. 
 
 Fig. B8, from an individual 60 mm. in length. 
 
 Fig. Ci — Hand (natural size) from C. whitmani. 
 
 Fig. C2 — First pair of abdominal appendages (1^) of 
 second-form male C. whitmani. 
 
 Figs. Di to D3 inclusive show chela, rostrum and first pair 
 of abdominal appendages of first-form males of the species 
 C. immunis. 
 
 Fig. Di — r, left chela, showing characteristic notch (n) 
 near the base of the movable finger ; r, typical C. immunis ros- 
 trum ; a, first pair of abdominal appendages. 
 
 Fig. D2 — c, right chela without characteristic notch near 
 base of movable finger ; r, rostrum, not noticeably different from 
 the rostrum shown in Fig. Di ; a, first pair of abdominal 
 appendages. 
 
 Fig. D3 — c, right chelae, showing characteristic notch (n) 
 near base of movable finger; c, left chela, without notch near 
 base of movable finger and smaller than the right chela ; r, ros- 
 trum, distinctly angled at the base of acumen; a, first pair of 
 abdominal appendages. 
 
 Fig. Ei — Hand from a first-form male 71 mm. in length. 
 
 Fig. E2 — Hand from a second-form male 71.5 mm. in 
 length. 
 
 Fig. E3 — Hand from a female 80 mm. in length. 
 
 Plate IV. 
 
 The figures in Plate IV. show comparisons between the 
 reproductive organs and first pair of abdominal appendages in 
 first-form and second-form males of C. virilis. All the repro- 
 ductive organs shown are drawn from crayfish which were 
 examined in June. 
 
 Fig. A — Reproductive organs from a second-form male 
 
 (52) 
 
without chelae, t, testes, the three lobes slender, without 
 secondary lobules ; v, vasa deferentia, long and convoluted. 
 
 Fig. Ai — First pair of abdominal appendages taken from 
 the same individual as the reproductive organs shown in Fig. A. 
 They are thick, have narrow bases and closely approximated 
 tips. 
 
 Fig. B — First pair of abdominal appendages of a second- 
 form male without chelae. Appendages are shown from the 
 ventral side. The bases are narrow and do not meet in the 
 median line. 
 
 Fig. Bi — Reproductive organs taken from the same indi- 
 vidual as the appendages shown in Fig. B. t, testes. The con- 
 nection between the lobes is very short and the two anterior 
 lobes are only imperfectly separated ; v, the vasa deferentia are 
 short and unconvoluted. 
 
 Fig. C — First pair of abdominal appendages of a second- 
 form male with chelae. The bases are broad and the tips widely 
 gaping. 
 
 Fig. D — Reproductive organs of a large first-form male. 
 t, testes. The lobes are large and full, and are distinctly sepa- 
 rated, anterior lobes unsymmetrical ; v, vasa deferentia, much 
 convoluted. 
 
 Figs. E, F and G are all taken from the same individual, 
 a large male with chelae. 
 
 Fig. E represents a side view of the first pair of abdominal 
 appendages after the first moult. 
 
 Fig. F represents a ventral view of the same appendages, 
 drawn in natural position. Note the closely approximated 
 bases. 
 
 Fig. G represents the same pair of appendages just after 
 second moult, showing transformation from second-form into 
 first-form. 
 
 Fig. H — Two views of a first abdominal appendage of a 
 second-form male with chelae. 
 
 Fig. I — Typical reproductive organs of a first-form male. 
 Lobes of the testes (t) widely separated and lobulated. 
 
 Fig. K — Chela (natural size) from a second-form male 
 after it had moulted three successive times into second-form. 
 Almost the entire growth had taken place within a single month. 
 
 Plate V. 
 
 Fig. A — Life-size drawing of C. ayersii. 
 Fig. B — Life-size drawing of C. whitmani. 
 
 (53) 
 
Plate VI. 
 
 A series of figures reproduced from photographs of crayfish 
 belonging to the species C. rusticus. Figures are about two- 
 thirds natural size. These photographs represent a graded 
 series of the species, showing variations in shape of rostrum and 
 chelae, in breadth of areola and in relative lengths of cephalo- 
 thorax and abdomen. 
 
 Fig, I — Male C. rusticus (according to Faxon C. neglectus). 
 
 Fig. 2 — Male C. rusticus (according to Faxon C. neglectus). 
 
 Fig. 3 — Male C. rusticus. Note that the differences 
 between Fig. 3 and Figs. 1 and 2 are not so great as are often 
 seen between individuals that are constantly classed as the 
 same species : e. g., in C. virilis. 
 
 Fig. 4 — Female C. rusticus. Body contour closely resem- 
 bles Figs. 1 and 2. Hands short and thick, as is usual in females 
 of any species of Cambarus. 
 
 Fig. 5 — Male, C. rusticus. The chief difference between 
 this figure and Figs. 1 and 2 lies in the rostrum, a feature which 
 is found to be very inconstant in any species. 
 
 Fig. 6 — Male, C. rusticus. Rostrum from the rostra shown 
 in Figs. 1 and 2, but not more different than from the rostra 
 shown in Figs. 4 and 5. 
 
 Fig. 7 — Male, C. rusticus. Rostrum and chelae both dif- 
 ferent from the rostrum and chelae shown in preceding figures. 
 
LIBRARY 
 
 OF THE 
 
 UNIVERSITY of ILLINOIS 
 
 Crayfish of Missouri 
 
 Plate I. 
 
Crayfish of Missouri. 
 
 Plate II. 
 
 M. Steele, del. 
 
LIBRARY 
 
 OF THE 
 
 UNIVERSITY of ILLINOIS 
 
 Crayfish of Missouri. 
 
 Plate III. 
 
 M. Steele, del. 
 
Crayfish of Missouri. 
 
 Plate IV. 
 
 KM. 
 
 £ ft 
 
 
 H 
 
 & 
 
 M. Steele, del. 
 
Note to the Reader: Plate V. is omitted but Fig". A is 
 printed as Fig-. 14 on Plate VI. Fig-. B is not given. 
 
 LIBRARY 
 
 OF THE 
 
 UNIVERSITY of ILLINOIS 
 
Crayfish of Missouri. 
 
 Plate VI. 
 
 <Q 
 
 C.auerjii 
 
 M. Steele photo fig-s. 1-13. H. Ayers, del. fig". 14.