EHINODON TYPICUS. 



pursues a waved direction, and at last is lost in, or coalesces with, the keel 

 on each side of base of caudal fin ; the upper again pursues a more direct 

 course, becomes forked posteriorly, and both its branches terminate under, and 

 anterior to, the second dorsal fin ; the keel on each side of the tail very strong 

 and thin at the outer edge. At the base of the upper lobe of the caudal fin, 

 there is a transverse groove, to admit of the ready elevation of the fin, a 

 power so necessary to direct the course of the fish in swimming. The first 

 dorsal fin, posteriorly, is deeply emarginate, and the second dorsal has its 

 inferio-posterior angle prolonged into a slender sharp point. Pectoral fins 

 large, and their hinder edge, towards its base, with a distinct, large, triangular 

 elongation. Ventral fins very small, and directly below the hinder portion of 

 the first dorsal ; anal fin also small, quadrangular, and with its superio- 

 posterior angle prolonged into a point, its anterior edge directly under the 

 hinder extremity of the base of the second dorsal. Caudal fin deeply forked, 

 the upper portion larger and much longer than the lower. Branchiae slightly 

 waved, the first and second much the longest, and, together with the third, are 

 in front of the base of pectoral fins ; the fourth and fifth are directly over it. 



P/iarpicc very large, and the inner extremity of each branchial canal ob- 

 structed by a sieve-like apparatus, consisting of a conjeries of cartilaginous 

 tubes closely set together, directed laterally, and the inner extremity of each 

 fringed with a delicate membrane offering an obstruction to the passage 

 of anything but fluid. (Esophagus rather narrow, and at its commencement 

 bends downwards towards the parietes of the abdomen, and forms nearly a 

 right angle with the fauces, which gives the fish the power of completely pre- 

 venting what enters its large mouth from being admitted into its stomach, un- 

 less desirable. The cardiac extremity of the stomach is very muscular, and the 

 inner surface is studded with hard pointed nipple-like bodies, all of which are 

 directed backwards, and offer an obstacle to the return of anything solid 

 from the stomach : the rest of the inner surface of the stomach and the small 

 intestines closely set with strong rugae, in the stomach oblique, in the intestines 

 nearly circular, and the latter, when about to terminate in the large intestines, 

 is also furnished with a number of nipple-like bodies, which prevent solids 

 from passing downwards. The termination of the small intestines is in the 

 form of a ring, which projects into the large bowels, and forms an effective valve 

 when any attempt is made to propel the contents of the large intestines back- 

 wards into the smaller ones. The inner surface of the former is furnished as in 

 other sharks, with a spiral band, the one side of which is loose, and by 

 this arrangement the alimentary fluid requires to pass over an extent of surface 



