NOTE ON THE CONUS ARTERIOSUS OF MEGALOPS 
 CYPRINOIDES (BROUSSONET) . 
 
 H. D. SENIOR, M.B., F.R.C.S. 
 
 [Reprinted from Biological Bulletin, Vol. XII., No. 6, May, 1907.] 
 
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NOTE ON THE CONUS ARTERIOSUS OF MEGALOPS 
 CYPRINOIDES (BROUSSONET). 
 
 H. D. SENIOR, M.B., F.R.C.S., . 
 
 Associate in Anatomy, Wistar Institute of Anatomy, Philadelphia. 
 
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 Since describing the conus arteriosus in Tarpon Atlanticus 1 I 
 have been fortunate in securing a specimen of Magalops cyprin - 
 6 'ides. For this I take the present opportunity of thanking 
 Professor David Starr Jordan. 
 
 The fish in question, preserved in alcohol, measures 19 cm. 
 (including caudal fin) so that the heart is extremely small, and is, 
 on account of its somewhat friable condition, difficult to handle. 
 
 The conus is everywhere quite obvious from the exterior. Fig. 
 1, drawn from the left side, indicates that the general form of 
 
 Fig. i. Fig. 2. 
 
 Fig. 1. Entire heart of Megalops cyprinoides from the left side, X 3 * A small 
 portion of the atrium has been removed to display the conus more fully. 
 
 Fig. 2. Frontal section through the right side of the heart of Me^alops cypri- 
 noides, showing the relations in the conus region, X IO - 
 
 conus and bulbus resembles that of Amia rather than that of 
 Tarpon. 
 
 The heart was opened by a mid-ventral sagittal incision, it having 
 been previously ascertained that such an incision would fall be- 
 tween the valves without cutting them. After examination and 
 
 1 Biol. Bull., February, 1907, p. 145. (The literature on the conus arteriosus 
 is given in this article. ) 
 
 Z G. 3 S 5 
 
379 
 
 H. D. SENIOR. 
 
 measurement the two halves were imbedded in celloidin and cut 
 into serial sections. 
 
 The extreme length of conus is I mm. in the mid-ventral line 
 and 1.5 mm. in the mid-dorsal and lateral lines. The ventricle, 
 from apex to junction with conus, has a mean measurement of 
 5.5 mm. The proportion in mean length of conus to ventricle 
 is therefore 1 to 4. 
 
 The conus contains two transverse tiers of valves, each tier 
 consisting of a right and left cusp placed symmetrically with re- 
 gard to the mid-sagittal plane. The general arrangement agrees 
 closely with that found in Tarpon , but the proximal cusps appear 
 to be proportionately more capacious. 
 
 The conus in Megalops not only projects more freely from the 
 ventricle than in Tarpon, but is of greater proportionate length. 
 It would seem to resemble more closely the conus of Albula (as 
 described by Boas, ’8o) except in the absence of the subsidiary 
 valve cusps of the latter. 
 
 It should be noticed that the heart described is from a young 
 fish, also that the measurements are, at best, approximate ; there- 
 fore, comparisons with adults of other genera, if pushed too 
 closely, are apt to be misleading. 
 
 The atrio-ventricular valve has three cusps. 
 
 A specimen of Chanos chanos (Forskal), for which I also have 
 to thank Professor Jordan, presents an easily recognizable ves- 
 tigial conus arteriosus, but only one tier of valves. 
 
 St. Louis, Mo., February 1, 1907. 
 
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