50 AN EXTRAORDINARY SHARK ; 



branchial aperture and is continuous and free across the 

 isthmus, forming a frill or ruffle ; it is held in place and 

 prevented from turning forward by a thin fold or wall of 

 membrane, near an inch in height, attached immediately 

 beneath the middle of the basihyal. The external distri- 

 bution of slime-canals is about as follows : starting above 

 the nostril in front of the eye a line turns backward along 

 each side of the skull and, after receiving a branch from 

 behind the eye, continues along the middle of each flank 

 to the extreme end of the vertebral column in the tail, 

 where it makes an abrupt turn downward for about a 

 quarter of an inch ; under the chin on each side, a line runs 

 along the mandible and curving upward disappears behind 

 the angle of the mouth ; a branch of this, beginning nearly 

 on a vertical beneath the middle of the space between eye 

 and nostril, runs farther from the mouth and turning up- 

 ward near the margin of the opercular flap after receiving 

 a short branch behind the angle of the mouth, continues to 

 a point a very short distance behind the spiracle, a small 

 branch coming into it near the end from the direction of 

 the corner of the mouth. Pectorals moderate, broad, 

 rounded. Dorsal comparatively small, its posterior ex- 

 tremity extending as far back as that of the anal, angle 

 blunt. The upper margin of the dorsal is armed with a 

 series of enlarged, compressed, chisel-shaped scales, which 

 extends forward on the back to a vertical from the vent, a 

 few of the anterior being horizontally flattened. Veutrals 

 large, broad a little broader than long, rounded, poste- 

 rior angle acute. Anal broad, long, rounded, acute-angled 

 posteriorly. Caudal long, very broad, rounded anteriorly, 

 posterior angle acute produced into a filamentary point, 

 margin very thin or membranaceous. Above the muscular 

 vertebral portion of the tail there is a narrow expanse of 

 fin, widening backward, the edge of which is armed by a 



