256 ZOOLOGY. 



tribe. The number of gill- apertures is five on each 

 side. The fins are short, and, for the most part, dis- 

 posed to a round form : the dorsal are two in number, 

 small, and placed far back; the tail-fin is unequally 

 divided, the upper being the longest and largest lobe. 



The head is flat. The snout prominent, rather 

 pointed, and has two nostrils at its extremity. There 

 is, also, on each side of the upper and back part of the 

 head, a large oval orifice, like a spiracle or nostril, pro- 

 vided with a valve, and communicating with a cor- 

 responding aperture in the roof of the mouth. The 

 mouth is capacious, and the dark skin around it is 

 incised on each side, to some extent beyond the com- 

 missure of the lips, exposing a white elastic membrane 

 beneath. The upper jaw is armed with many rows of 

 small sharp teeth, while the lower has only a single 

 row of perpendicular teeth, or rather, an elevated plate 

 of bone, sharply toothed on its summit, and bearing a 

 close resemblance to a segment of the surgical circular 

 saw called a trephine. The eyes are much more promi- 

 nent and dilated than is usual with sharks ; the iris 

 is black; the pupil transparent, and of a greenish 

 colour. 



The example I dissected was a female. The abdomen 

 contained six round membranous eggs, each the size of 

 a pigeon's egg, and containing a colourless glairy fluid. 

 The two uteri were empty and collapsed. The principal 

 peculiarity in the anatomy of this shark is the existence 

 of what must be regarded as a sternum, or breast-bone, 

 (which is by no means common, even in bony fishes.) It 

 is a small bone, shaped like a horse's hoof, and has two 

 processes projecting laterally, by which it is articulated 

 to the bones supporting the pectoral fins. The hollow 

 of the hoof (to pursue the comparison) is closed in- 



