Dog-fish. 



PIKED DOG-FISH. 37 



section ; the mouth is gently arched and the snout obtuse. The 

 pectoral fins are not notched at their bases, and are not produced 

 forward. There is no nictitating membrane ; the gill-slits are 

 small and lateral in position. Remains of Sharks of the family 

 Spinacidas are not found in strata below the Upper Cretaceous. 



Valentin's Sea-hound, Scymnus lichia, 73, is a fish common in 

 the Mediterranean and on the coast of Portugal, and occasionally 

 met with in the English Channel. The dorsal fins have no spines 

 and the first is set well in advance of the pelvic fins. The upper 

 teeth are small and pointed ; the lower teeth are much larger than 

 the upper teeth (see jaws 74), they are broad and compressed, 

 triangular and erect, but slightly sloping in the young. 



The Piked Dog-fish or Spiny Dog-fish, Acanthias vulgaris, 75, Piked 

 has a spine in the anterior edge of each of the dorsal fins (see spines 

 76). The teeth are similar in the upper and lower jaws ; they are 

 rather small, triangular, and compressed, with the apex much 

 turned aside, so that the inner mai'gin of the tooth forms a 

 cutting edge (see jaws 78). Although the tail fin is not 

 symmetrical above and below the middle line the vertebral column 

 is not uptilted (see tail 77) . The Piked Dog-fish has a remarkable 

 distribution, being found in the temperate seas of the northern and 

 southern hemispheres, but not in the intermediate tropical region. 

 It is one of the commonest Dog-fishes around the British coast, and 

 causes much trouble to fishermen by cutting their lines and carry- 

 ing away the hooks. 



The Black Dog-fish, Spinax niger, 79, is a small Dog-fish found 

 in most European seas, and common off Portugal and in the 

 Mediterranean. This fish is apparently not black when alive ; 

 freshly taken specimens are very pale in colour (see sketch 98, in 

 Cabinet-case 44, Deep-sea Fishes). The centra (see 80 in Wall- 

 case 2) possess no secondary calcifications, but only the primitive 

 double-cone calcification immediately surrounding the constricted 

 notochord. This type of vertebra is termed ' cyclospondylic/ and 

 is characteristic, among modern fishes, of the Spinacidse, although 

 it occurs in the more primitive extinct members of other families, 

 e. g. in the Liassic genus Palaospinax, supposed to belong to the 

 family Cestraciontidse. 



The genus Centrophorus includes deep-sea Sharks growing to 

 about five feet in length. Most of them are caught off the coasts 



