138 CLASSIFICATION OP FISHES. 



to mark the primary distinctions of the two typical 

 groups. This character also happens to be one of the 

 most obvious ; and thus affords the ichthyologist an 

 easy and^ as we believe, a natural guide among the in- 

 tricacies of the numerous genera that have been formed 

 out of these fishes. On looking to these, we plainly 

 perceive that, although they have hitherto all been 

 termed genera, and therefore placed upon the same rank, 

 yet that some are much more strongly marked in their 

 differences than others; so that they form themselves 

 into little groups, under which two, three, or more, may 

 be arranged. This it would be very easy to accomplish, 

 if our object was merely to make an artificial arrange- 

 ment : but when we attempt to work out a natural 

 group, such is the state of ichthyological science, that it 

 almost becomes absolutely necessary to verify what has 

 been done by our predecessors, by going over the same 

 ground, and re-examining the major part of these sub- 

 genera ourselves. In very many instances, however, 

 this is totally impracticable ; and in such cases we have 

 no other resource left than to take for granted what has 

 been published, and endeavour to trace the line of affi- 

 nity by the imperfect materials before us. In the at- 

 tempt, therefore, which we shall now make to place the 

 numerous sub-genera of sharks under their genera, pro- 

 perly so called, the above difficulties must be borne in 

 mind, and every allowance may fairly be claimed for those 

 errors which necessarily attend upon a task so peculiarly 

 perplexing. Enough, however, will come to light in 

 the sequel, to show that this effort has not altogether 

 been unsuccessful ; and for the rest, we must leave the 

 rectification of minor errors of location to time, — to 

 greater knowledge of those forms already known, but 

 imperfectly described, — and to the discovery of others 

 which are at present unknown. 



(121.) The first genus, if such it be, which we shall 

 notice, among the SquaIi7i(B, or sharks having no tempo- 

 ral orifices, is that of Scoliodon of Muller and Henle, 

 which seems to bear a nearer affinity than any other to 



