XVII ELASMOBRANCHII — SELACHII 449 



to reach a length of 15 to 20 feet. The geiuis Gcileus includes 

 the small Sharks commonly known as " Topes," which are 

 common in nearly all tropical and temperate seas. The British 

 species, G. canis, which ranges from 4 to 6 feet in length, is a 

 bottom-feeding Fish, preying on Molluscs, Crustacea, Star-Fish, 

 and small Fishes. The various species of Jlfustehis, or " Hounds," 

 resemble the Topes in their habits and distribution. Living 

 principally on jMoUuscs and Crustaceans, the dentition has lost 

 the trenchant, unicuspidate type characteristic of most other 

 Carchariidae, and is adapted for crushing and grinding, the teeth 

 being iiat, without cusps, and arranged in pavement-like rows. 

 Two species, M. vulgaris and M. laevis, are abundant on the 

 coasts of Europe and the British Isles. Scylliogaleus, which com- 

 bines the general characters of Mustelus with nostrils similar to 

 those of a Scyllium, is known only from a single specimen from 

 the coast of Natal.^ 



The Carchariidae are comparatively modern Sharks. No 

 undoubted remains are known earlier than the Eocene, in which, 

 as in the succeeding Miocene and Pliocene deposits, they are 

 represented principally by their characteristic teeth. The extinct 

 fossil genera are few in number, and so far as their dentition is 

 concerned they differ but little from their living allies. 



Fam. 9. Sphymidae (Hammer - head Sharks). — In their 

 general characters the Hammer-head Sharks agree with the 

 Carchariidae. They are distinguished, however, by the remark- 

 able shape of the head, which is prolonged into two conspicuous 

 lateral lobes, supported internally by corresponding cartilaginous 

 outgrowths from the post-orbital and the lateral ethmoidal or 

 nasal regions of the skull, with the eyes at their distal extremities, 

 and- the nostrils in relation with their anterior margins. One 

 genus and five species. 



The Sphyrnidae are denizens of nearly all tropical and sub- 

 tropical seas. Spliyrna {Zygaena) tudes occurs in the Mediter- 

 ranean, and S. zygaena is a very rare visitant to the British coasts. 

 A specimen over 13 feet in length was captmed at Ilfracombe 

 in 1865, and other examples have been taken off Banffshire, at 

 Newlyn in Cornwall, at Yarmouth, and in Carmarthen Bay." 

 The shape of the head differs in different species, and in young 



1 Boulenger, Ann. Mag. Nat. Hist. (7), x. 1902, p. 51. 



2 Day, British Fishes, London, 1880-84, ii. p. 294. 



vnT, VTT 



2 G 



