16 BULLETIN OF THE 



The Cartilages of the Tail. 



Plate XIV. Fig:. 1. 



Below the vertebrae the series of radials of the caudal fin begins con- 

 siderably in advance of the fin itself, over the hinder portion of the anal. 

 (PI. XIII. c-c.) Posteriorly they have the appearance of being formed 

 by downward growth of the hsemapophyses, separation or segmentation 

 from which only obtains in twenty-one of the anterior. The lines in the 

 sketch, which might be taken as separations in the others, only serve to 

 show the course of the vessel enclosed by the transparent cartilage. 



The upper series of the radials of the caudal begins under the extrem- 

 ity of the dorsal fin. For a short distance in front, not shown in the 

 sketch, the series is separated by a space from the neural intercalaria, 

 as if the radials had originated like those of the dorsal and anal, inde- 

 pendently, and afterward through downward growth had in the greater 

 portion of the extent come in contact with the neural processes. These 

 radials and the interneurals are not fused like the radials and haeraa- 

 pophyses. They retain a considerable size at the end of the vertebral 

 column. 



TJie Brain. 



Plates XV. and XVI. 



The brain is very small. Comparatively the amount of fore-brain is 

 much smaller than in the higher sharks, Carcharias, Zygsena, and others. 

 In outlines and proportions there is great similarity between this brain 

 and that of the Notidanidae. In both of the genera of that family 

 the brain is equally elongate, and the disposition of the nerves is not 

 greatly different ; the differences are mainly in details rather than in 

 general build. Owing to the softness of the mass, when removed from 

 the skull, it collapsed and spread out so that the figures sketched are a 

 trifle more broad and flattened than is natural. The condition prevented 

 such a removal of the envelopes as was desirable. The olfactory lobe 

 is shorter than that of Hexanchus (compare Maclay, Das Gehirn der 

 Selachier, Plate II.). The olfactory bulb is similar in shape in these 

 genera ; it is a club-shaped expansion with lobules at the end from which 

 the nerve distribution takes place. Being broader in front, the hemi- 

 spheres taper more toward the hypophysis than is the case in Hexanchus. 

 As in the latter, the optic lobes are rounded above and in front, and are 

 — when viewed from above — about half exposed. 



