ir. VEBTEBRATA: PIISCES, SELACHII. 



571 



Sub Order II, SQUALI (Euselaohii). Normul sharks, with cylindrical 

 bodies, free thoracic fins, heterooercal tail, lateral gill slits. Most of them 

 are fast swimmers and are rapacious, the teeth being usually pointed, with 

 sharp or toothed edges, but in some the teeth are pavement-like and are 

 used for crusliing sliell fish. The numerous families are distinguished by 

 vertebral characters, number of dorsal fins, presence of nictitating mem- 

 brane, etc. In the Galeid^, in which the nictitating Diembrane is 

 present, belong, besides the dog-sharks (Mustelus*&XiA Oaleus*), the largest 

 of all sharks, Carcharinas* some of which have man-eating reputations. 

 The hammer heads (^//(/ce»a*) are closely allied. The mackerel sharks 

 Lamiia *) and tlje great white ' man-eater,' Carcltarodon* lack nictitating 

 membranes. All of the foregoing have star-shaped figures in the verte- 

 brae (p. 570). In the dog-fishes, represented by Acanthias vulgaris* (or 

 Hqualas acanthias, fig. 598), there is a spine in front of each dorsal fin. 



Sub Order III. RAI^. In the skates the body is flattened liorizontally 

 fig. 599), and the pectoral fins, also flattened, are united to the sides of 



Fig. .539.— flfiia bnd.s, ™ale, ventral view. (After Mobius and Heincke.) B. ventral, 

 Be, pectoral fin; Jil, rostrum; n, anu.s: c copulatory part of ventral; As, gill clefts; 

 7/1, mouth; /(, nostril; between ttiem the oronasal groove. 



the body, the union usually extending clear to the tip of the snout, and 

 frequently back to the pelvis, giving the body a rhombic appearance from 

 above. The animals swim by undulating motions of tliese fins. They 

 mostly lie quiet on the bottom, and hence the lower surface is white, 

 the upper colored. The union of the fins to the side has resulted in trans- 



