SHARKS AND RAYS. 519 



carrying a large number of cusps, these latter gradually diminishing in height 

 from one end of the tooth to the other. The notochord remains in its 

 original condition throughout the greater part of the backbone. These 

 sharks, which may grow to about fifteen feet in length, are to be found in 

 most of the warmer seas. In the second genus, Chlamydoselache, which is 

 represented only by a single species from the Japanese seas, the six gill-slits 

 have frill-like expansions of skin on their margins, the teeth are of simpler 

 structure, and the body is so long and slender as to be almost eel-like. 



SUB-ORDER II. TECTOSPONDYLI. 



In this sub-order which includes the spiny dog-fishes, saw-fishes, and the 

 rays the vertebrae, when fully developed, have their calcareous plates so 

 arranged that in cross-section the circular ones predominate over those that 

 radiate from the centre to the circumference. None of the members have an 

 anal fin, but the spiracles are large. In the rays the body is characterised by 

 its extreme depression, and the pectoral tins are developed into huge flaps 

 bordering its sides. 



While agreeing with the other members of the sub-order in the structure 

 of the vertebrae, the species forming the family tfpinacidce are externally like 

 sharks. The gill-clefts are small and lateral in position, the 

 spiracles are situated behind the eyes, and there are two Family 



dorsal fins, which may be furnished in front with spines. In Spinacidce. 

 addition to the typical genus Spinax, the family includes the 

 spiny dog-fishes (Acanthia&), taking their name from the presence o* spines to 

 the dorsal fins, and likewise the Greenland shark (Lcemargus), Whereas the 

 spiny dog-fishes do not exceed about four feet in length, the latter species 

 grows to as much as fifteen, and has no spines to the tins of the back. It has 

 a peculiarly tuberculated skin ; and whereas the upper teeth are small, those 

 of the lower jaw are taller, and have their tips bent to one side. Nearly 

 allied is the spiny shark (Echinorhinus) of the Atlantic and Mediterranean, in. 

 which the upper and lower teeth are alike. 



The monk- or angel-* sh (Squatina vulgaris) is the sole member of a family 

 which serves to connect the last with the true rays. This ugly fish has a 

 depressed skate-like body, but a nearly terminal mouth, and 

 the pectoral tins not connected at their bases with the head. Family 



The conical teeth are sharply pointed, the gill-slits are lateral, Squatinidce. 

 the skin is tuberculated, and the dorsal tins, which have no 

 spines, are placed on the tail. The monk-nsh reaches a length of fully five 

 feet, and is found in nearly all seas. 



The production of the extremity of the upper jaw into a long, flattened 

 bony process, armed on each side with sharp quadrangular teeth set in 

 sockets, serves at once to distinguish the saw-tishes from all 

 their kindred. They form two genera Pristiophorus and Families 

 Pristis each of which is regarded as representing a family Pristiophoridce 

 by itself, although such a division certainly seems somewhat and Pristidce. 

 superfluous. The members of the first genus are relatively 

 small fishes from the seas of Australia and Japan, characterised, among other 

 features, by the lateral situation of the gill-slits, and the possession of a pair 

 of tentacles arising from the middle of the jaw, and projecting far beyond the 



