368 AMERICAN TESTUDINATA. Part II. 



of the North American Turtles should at once meet with a favorable reception. 

 There are so many naturalists who look upon classification in general, and especially 

 upon minor subdivisions, in the system of animals, merely as convenient devices 

 to facilitate their study, that any distinction which in their estimation might be 

 dispensed with is considered by them as objectionable, and must be so, according 

 to their standard, which does not even admit that genera may exist in nature. 

 However, as it is one of the objects of this work to show that genera are 

 founded in nature, and that therefore the investigation of the genera and all 

 the other natural divisions among animals require as careful and minute atten- 

 tion as that of species, I would add a few more remarks upon this topic, in 

 order to anticipate the objections which may be raised against the subdivision 

 of our Turtles into many distinct genera, and to illustrate their value by a com- 

 parison with the genera of one order of the class of Birds, — the Birds of prey, — 

 with which the Testudinata may fairly be contrasted for their number, and the 

 character of their peculiarities. In the first place, the groups called by Dumeril 

 and Bibron Thalassites, Potamides, Elodites, and Chersites (without entering again 

 into the question already discussed,^ whether they are families or groups of a 

 higher order, or partly families and partly sub-orders) may stand a comparison 

 with those groups among the Birds of prey which correspond to the old genera 

 Vultur, Falco, and Strix, and which are now generally considered as fiimilies, 

 though the diflerences among these Birds are certainly not so great, nor even of 

 the same kind, as those which distinguish the Chelonii and the Amydte. Indeed, 

 the Vulturidae, Falconidre, and Strigida?, when contrasted with one another, exhibit 

 rather differences of form than of structure, whilst the peculiarities of the sub- 

 divisions of Testudinata cited above are rather differences of structure, which 

 amounts to saying, that the differences of the latter bear the character of sub- 

 orders, and the groups of Birds mentioned before differ in the manner of fam- 

 ilies. And yet nobody objects now any longer to the further subdivision of the 

 Falconidre, for instance, into such sub-families as Aquilina^, Eagles, Buteonina^, Buz- 

 zards, Falconinge, Falcons, Accipitrinaj, Hawks, etc. This being the case, who does 

 not perceive, that, if the groups FalconidiB, Vulturidte, and Strigida? are genuine 

 families, they ought not to be compared respectively with a group hke the Elodites, 

 which embraces animals as different as the Cistudo, the true Emys, the Terrapins, 

 the Cynosternum, the Chelydra, the Chelys, the Chelodina, etc.; but that, on the 

 contrary, groups like these last, well circumscribed within their natural limits, 

 truly constitute famihes also, corresponding, by their intrinsic value, to the families 

 of the Strio-idsB, Vulturidie, and Falconidas. 



o 



1 Comp. Chap. 1, Sect. 2, p. 242-252. 



