XVII ELASMOBRANCHII—SELACHII 449 
to reach a length of 15 to 20 feet. The genus Galeus 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 Molluses, Crustacea, Star-Fish, 
and small Fishes. The various species of J/ustelus, or “ Hounds,” 
resemble the Topes in their habits and distribution. Living 
principally on Molluscs 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 flat, without cusps, and arranged in pavement-like rows. 
Two species, J. vulgaris and JL laevis, ave abundant on the 
coasts of Europe and the British Isles.  Scylliogalews, which com- 
bines the general characters of JZustelus 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 httle from their living allies. 
Fam. 9. Sphyrnidae (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. Sphyrna (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 captured 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. 
* Day, British Fishes, London, 1880-84, ii. p. 294. 
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