144 CLASSIFICATION OF FISHES. 



midical snout^ and somewhat in its teeth, is at once dis- 

 tinguished from that suh-genus by its lengthened and 

 unequally lobed tail^ which has the same form as in the 

 generality of sharks ; like them^ also^ it has two sof 

 dorsal^ and one anal fin. The long snout seen in Isu- 

 Tus, appears to be^ in some measure, continued in one 

 of the sub-genera (^Pristiurus Bon.) which authors 

 have placed under Scyllium. These smaller divisions 

 have been chiefly formed upon the different positions of 

 the dorsal fins^ and other minor characters, •which, how- 

 ever important and interesting they may be thought, do 

 not appear to us, taken by themselves^ to lead to any 

 clear notion on the natural sub- generic types of the 

 group before us. As we shall notice them in our 

 synopsis, we need not, in this place^ detail their technical 

 characters. 



(126.) The genus Galeus has an obvious and close 

 affinity to that oi Scyllium. They are almost exact pro- 

 totypes of the true sharks, except in wanting the tem- 

 poral spiracles : all the teeth are flat and sharp ; but 

 they vary so much in their minor modifications, that 

 Muller and Henle have divided this group into four 

 sub-genera, viz. Galeocerdo and Galeus, where the 

 teeth are serrated (2 species) ; Loxodon, having no 

 serratures (1 species) ; and TriacMs, with the teeth 

 pointed, as in Scyllium, and without a dimple at the 

 tail (1 species). The value of these distinctions will 

 no doubt appear more definite, when the learned and 

 able ichthyologists who have proposed them, pubHsh 

 their views more in detail : until then we feel incom- 

 petent to arrive at any conclusion on the subject. 



(127.) The third genus, Centrina, is much more 

 definite than the two last, and seems to be the most 

 natural in the present sub-family. It is composed of 

 all those spiracled sharks which have a spine placed 

 before each of their dorsal fins, while the anal fin is 

 entirely wanting : hence it differs from every other 

 group in this sub-family. But this structure is not 



