150 The West American Scientist. 



terior margin of anal; the rest of the body without villi or 

 prickles. Lateral line complete. Ventrals reaching ^-^ to vent, 

 which is nearer to base of caudal than to tip of snout, otherwise 

 as insemiscabra. 



THE YOUNG STAGES OF SOME SELACHIANS. 



Squalus acanthias L. Captain Carter of the Azalene ob- 

 tained the young of this species from its mother in August. They 

 were far along in their developement. 



Total length .22 m; dimensions of the yolk. 02 x. 04 m The 

 upper surfaces are blue, the lower white; a series of white spots 

 along the sides. A light streak en sides above the ventrals. An- 

 terior portions of dorsals black, the posterior margin and tip 

 white. Upper margin of caudal and anterior margin of its lower 

 lobe white; tip of upper lobe black; a white and then a black band 

 between the black tip of the upper lobe and the anterior margin 

 of the lower lobe. Upper basal portion of ventals dark blue, the 

 remainder of the fin white. Pectorals largely blue above, the 

 posterior margin being white, their lower surfaces largely white 

 a median blue spot on its outer half. Snout broad and rounded. 



Triacis semifasciatus Girard. A female of this species 

 about 1.5 m. long, caught Sept. 6, 1889, contained a number of 

 young measuring .095-. 105 m. Each embryo is surrounded by 

 a delicate membrane filled with a hyaline watery albumen. The 

 yolk is pyriform and measures .03 x. 07 m. In the smallest indi- 

 viduals the external gills are still present; the spiracular gills 

 have, however, disappeared. In the proportions, position of find 

 and coloration these embryos greatly resemble the adult. The 

 asperities of the skin are entirely wanting. The ventral surface 

 with the paired fins, the anal and lower lobe of the caudal are 

 plain. A dark cross bar between the spiracles; three crossbars 

 iDetween this and the first dorsal fin, one on the middle of the first 

 dorsal, another at its posterior margin, two between the dorsals, 

 a dark cross bar on the anterior and posterior margins, of the 

 second dorsal, four behind the second dorsal fin. In the larger 

 specimens there is a spot on the middle of the lower caudal lobe 

 and two or three along the sides anteriorly. The remaining 

 color marks of the adult are not yet developed. 



Rhinotriacis HENLEiGill. A specimen of this species about 

 1.5 m. in length was caught off the wharf Sept. 7th, 1889. It 

 Contained six young, three in either uterus. They are .115 m. 

 long and possess most of the characters of the adult. The tips 

 of the caudal and dorsal fins and a median dorsal band behind 

 the second dor.sal are dark blue, otherwise the embryos are color- 

 less. The external gills have disappeared. The umbilicus is 

 very long .14 m. The yolk is bright yellow; it is intimately con- 

 nected with the walls of the uterus. As the young of this species 

 are attached by a placenta it may be generically distinguished 

 Triacis from in which the young are free. 



