164 CLASSIFICATION OF FISHES. 



of one, correspond to those of the other, — but with 

 this difference_, that all of one are furnished with tempo- 

 ral spiracles^ which spiracles are not seen in the other. 

 Having, therefore^ endeavoured^ in the first instance, to 

 make out the affinities of each among themselves, we then 

 select, from all the minor groups that have been named^ 

 those which correspond, in some way, to each oth^r : 

 these we denominate genera, and place all the others as 

 sub-genera : the distinction, therefore, is neither empy- 

 rical nor arbitrary; however we may err in the selection, 

 the principle upon which that selection has been made 

 is sound and philosophic. We have little doubt that 

 nearly all the divisions of Rafinesque, Cuvier, Muller, 

 Henle, Smith, Le Sueur, &c. wiU arrange themselves 

 in the line of affinity, either as genera, sub-genera, or 

 aberrant species : but we repeat our belief, that our 

 existing information on this family is not sufficient to 

 carry us through such an analysis. By far the 

 greater part of the specimens of sharks, seen in mu- 

 seums, are miserably preserved, — the natural form 

 completely destroyed by having the skin either dilated 

 or contracted ; while the mouth is either closed, so that 

 the teeth are not seen, or the jaws are taken out, or the 

 specimens are of young individuals before the teeth are 

 weU developed. We look forward, indeed, with much 

 interest to the forthcoming publication of MM. Muller 

 and Henle upon this family, satisfied that in many re- 

 spects it will add much to our general knowledge of this 

 group. But we consider the principles of their arrange- 

 ment, so far as it has been developed, as essentially 

 artificial, being framed without any regard to the other 

 groups of ichthyology ; and we look on all systems 

 founded, as this is, upon the teeth, as hable to much 

 fallacy, because these organs are weU known to vary in 

 young and adult specimens, as well as in mature old ones, 

 of species which follow close upon each other in all the 

 remaining points of their organisation. Our chief desi- 

 derata, in fact, are accurate drawings, and full descrip- 

 tions, made from the fresh subject, and from adult 



