SELACHOIDEI. 331 



occurs at Lyme Eegis ; its skin is granular ; each dorsal fin 

 possesses a spine ; the teeth in the jaws are dissimilar — the 

 upper being multicuspid, longitudinally ribbed as in Hybodus, 

 the lower smooth and tricuspid. Drepanophorus and Spinax 

 primcevus occur in Cretaceous formations of England and the 

 Lebanon. 



Centeina. — Each dorsal fin with a strong spine. Trunk rather 

 elevated, trihedral, with a fold of the skin running along each 

 side of the belly. Teeth of the lower jaw erect, triangular, finely 

 serrated ; those of the upper slender, conical, forming a group in 

 front of the jaw. Spiracles wide, behind the eye. 



One species, Centrina salviMii, from the Mediterranean 

 and neighbouring parts of the Atlantic ; of small size. 



AoAKTHiAS. — Each dorsal fin with a spine. Teeth equal in 

 both jaws, rather small ; their point is so much turned aside 

 that the inner margin of the tooth forms the cutting edge. 

 Spiracles rather wide, immediately behind the eye. 



The two species of " Spiny Dog-fishes," A. vulgaris and 

 A. hlainvillii, have a very remarkable distribution, being 

 found in the temperate seas of the Northern and Southern 

 Hemispheres, but not in the intermediate tropical zone. 

 They are of small size, but occur at times in incredible 

 numbers, 20,000 having been taken in one sean on the 

 Cornish coast. They do much injury to the fishermen by 

 cutting their lines and carrying off their hooks. 



Centrophorus. — Each dorsal fin with a spine which, however, 

 is sometimes so small as to be hidden below the skin. Mouth 

 wide. Teeth of the lower jaw with the point more or less in- 

 clined backwards and outwards. Upper teeth erect, triangular, 

 or narrow, lanceolate, with a single cusp. Spiracles wide, behind 

 the eye. 



Eight species are known from the southern parts of the 

 European seas, and one from the Moluccas; they do not 

 appear to exceed a length of five feet. According to the 



