THRESHER. 



33 



some of the extinct species of Carcharodon must have been vastly 

 larger, judging by the great size of the teeth (e. g. 43) that are 

 found in Eocene, Miocene, and Pliocene strata. 



The Thresher or Fox Shark, Alopecias vulpes (1 139, hanging from Thresher. 



Fig. 18. — Thresher Shark, Alopecias 



the rail opposite Wall-Case 3, and fig. 18), has an extremely long 

 tail fin, and has not the paired longitudinal keel at the side of the 

 tail that is present in the Sharks of the two preceding genera. 

 The Thresher is common on the British coasts ; it feeds on 

 Herrings, Pilchards, and Sprats, and attains to a length of fifteen 

 feet, one half of which is taken up by the tail. 



In the genus Odontaspis (46, and specimen 1123, hanging from 



the rail opposite Wall-case 20) the second dorsal fin and the anal 



fin are not so reduced in size as they are in the genera Lamn,a, 



Carcharodon and Alopecias, and there is no tip on 



A the upper surface of the root of the tail. The teeth are 

 long and lanceolate, with one or two small cusps at the 

 base of the main cusp (see jaws 47, and fig. 19). 

 The Elfin Shark, Mitsuhurina owstoni, is closely 

 allied to Odontaspis, but diners in the shape of the 

 snout, which projects beyond the jaws to a considerable 

 extent (see 1124, hanging from the rail opposite Wall- 

 case 19). It is even more closely allied to the extinct 

 Scapanorhynchus of the Upper Cretaceous strata of 

 Syria. The Elfin Shark is a deep-sea Shark first 

 caught in the year 1898 in the seas of Japan. The 

 tail is longer than that of Odontaspis and is nearly in a line 

 with the body. The Shark grows to about twelve feet in length. 



The Basking Shark, Selache maxima or Cetorhinus maximus 

 (see fig. 2, p. 8), is a great Shark growing to 33 feet or more, 

 and widely distributed in northern seas. In Wall-case 1 the Shark 



D 



Fig. 19. 



Tooth of 



Odontaspis 



elegans. 



Elfin 

 Shark. 



Baskim 

 Shaik. 



