53o SHARKS AND RAYS. 



Represented in British waters by the larger (Scy ilium canicula), 

 True Dog-Fishes. . . 



and lesser spotted dog-fish (S. catulus), this genus is characterised by 



the first dorsal fin being above or behind the line of the pelvic pair ; by the origin 



of the anal being in advance of the line of that of the second dorsal ; the absence 



of serration of the upper edge of the caudal fin ; and the small and delicate teeth, 



which are arranged in numerous series, and generally have a long central cusp, 



flanked by one or two small ones on each side. About half a score of species have 



been described, ranging over the coast-regions of most temperate and tropical species, 



and all of comparatively small size ; the majority having prettily spotted skins. 



Their food consists mainly of crustaceans and molluscs ; and their flesh is eaten 



not unfrequently by fishermen, while in the Orkneys, where the British species are 



more abundant than elsewhere, it is regularly dried for winter consumption. The 



shagreen of their skins is also employed in wood-polishing. These sharks lay eggs 



of the form shown in our illustration. Fossil dog-fishes date from the period of 



the Chalk ; and they are represented in the Kimericlge Clay by the extinct 



Palceoscyllium, in which the origin of the second dorsal fin is placed in advance of 



that of the small anal. 



Among several allied genera we may especially notice the zebra- 

 other Genera. a • • 



shark (Stegostoma tigrinum) of the Indian Ocean, attaining a length 



of from 10 to 15 feet, and noticeable for its handsome coloration, which consists of 

 a brownish yellow ground-colour, marked with black or brown transverse bars 

 or round spots. In this fish the first dorsal fin is above the line of the pelvic pair, 

 while the second is in advance of the line of the anal, which is approximated to 

 the caudal ; the latter being greatly elongated, and equal to half the total length. 

 Young specimens of this shark are generally met with near the coast, but the 

 adults are more or less pelagic. Dog-fishes of smaller size from the Indian Ocean 

 constitute the genus Chiloscylliwm, in which the first dorsal fin is either above or 

 behind the line of the pelvics ; while the anal is far behind that of the second 

 dorsal, and close to the caudal ; the teeth being small and triangular, with or 

 without lateral cusps. The existing species are very handsomely ornamented with 

 dark bands and spots. In a fossil state the genus has been recorded from the 

 Miocene Tertiary. Three bottom-haunting sharks from the Japanese and Australian 

 seas have been described under the name of Crossorhinus, and are remarkable for 

 the presence of leaf -like expansions of the skin on the sides of the head. As in 

 the case of other fish similarly adorned, these structures are probably for the 

 purpose of attracting prey ; and in order that they may be well concealed, these 

 sharks have a coloration closely assimilating to that of a rock covered with sea- 

 weed or corallines. 



The Pavement-Toothed Sharks, — Family Cesteaciontid^e. 



The well-known Port Jackson shark (Cestracion pliilippi) and three allied 

 species are the sole existing representatives of a family which was exceedingly 

 abundant during the Secondary epoch. They differ from all the foregoing in 

 the presence of a strong spine on the front edge of each of the two dorsal fins. 

 The first dorsal fin is situated above the space between the pectoral and pelvic 



