158 CLASSIFICATION OF FISHES. 



analogies of the Sturionidce have been already stated , 

 but we may remark, that the smallness of their mouths 

 is in complete accordance with that structure which is 

 one of the most marked pecuHarities of the Grallatores, 

 or wading birds ; while the order Edentates, among 

 quadrupeds, — the types of which have their bodies co- 

 vered with bony scales like the sturgeons^ — is an indirect 

 proof in support of the opinion that all are repre- 

 sentatives of each other. Lastly^ the Polyodonidce , and 

 the natatorial type of birds^ are those only which have 

 the snout or bill excessively broad and uncommonly 

 flattened. That Polyodon, therefore, is the natatorial 

 and, consequently, the fissirostral type of the cartilaginous 

 circle, cannot be doubted, because its snout is much 

 longer and broader than in any other fish yet disco- 

 vered ; and we thus get an explanation why, in a group 

 which is collectively a natatorial type, it should yet 

 have one of the peculiarities of that type so pre- 

 eminently conspicuous. 



(1S9-) To trace the analogies of the cartilaginous 

 families further, might weary the reader, and may be 

 thought unnecessary by the naturahst ; seeing that all 

 the pecuHarities of the two most singular forms in the 

 group, Polyodon and ChimcEra, turn out to be in per- 

 fect accordance with those ordinary laws of variation 

 which nature adheres to in other divisions of the ver- 

 tebrated animals, and which we hope to trace hereafter 

 in the annulose circle. There can be no doubt that 

 innumerable analogies, equally strong, exist between 

 them and their representatives among the osseous fishes, 

 which may hereafter add additional force to what has 

 just been elucidated. 



(140.) The analogical relations of the primary divi- 

 sions of the order being now disposed of, we shall again 

 revert to the family of Squalidcs, for the purpose of 

 ascertaining whether the same system of representation 

 can be traced in its sub-families. In endeavouring to 

 determine these latter, it will be remembered that we 

 have noticed them in the following order : ZyganiruB, 



