Chap. III. GENERA AND SPECIES. 369 



This is the pasition whicli I am prepared to sustain by a further comparison. 

 But even if the Thalassites and Am^-daj were genuine llunilies, and not sul)-oiders, 

 this would not constitute an objection against suljdividing them farther into minor 

 natural groups, any more than the nature of the type of Falconidai constitutes an 

 objection against subdividing them into sub-families like those mentioned above, each 

 of which contains still a number of distinct genera. Let us take, for instance, the 

 group of our Terrapin.s, all of which are now generally I'eferred to the genus Emys. 

 It contains a great many species, which in the ultimate details of their structure 

 differ as much, if not more, one from the other, than any two genera admitted 

 among either the Falconidte, the Vulturida), or the Strigidte. I am willing to stake 

 the correctness of my views on this whole subject upon one single case, taking as 

 an example Emj^s rugosa (rubriventris,) mobiliensis, and concinna, (floridana,) which 

 together constitute, in my opinion, a natural genus, and comparing them with 

 any other natural group of species of tliis very same type, as for instance Emys 

 scabra (serrata,) Troostii, and elegans (cumberlandensis,) taken together as another 

 genus ; or Emys picta, Bcllii and oregonensis ; or Emys geographica, and LeSueurii ; 

 or Emj-s concentrica, or insculpta, or marmorata, or reticulata, or guttata, or Miih- 

 lenbergii, which constitute singly as many natural genera. Any zoologist, who, 

 after a thorough comparison of the external characters and of the skeletons of 

 the three firstruamed species, (Emys rugosa, mobiliensis, and concinna,) taking 

 especially into account their skulls, their jaws, and their feet, and contrast- 

 ing them with those of Emys picta and oregonensis, or of Emys in.sculpta, or 

 any other of the groups of species just named, — any zoologist, I say, who, 

 having made such a comparison, would deny their generic difference, must be 

 either blinded by prejudice against truth, or incapable by natm'e of applying him- 

 self to higher questions in Natural History. If this be true, it follows that among 

 the Testudinata most of the genera contain very few species, and that this order 

 affords an excellent opportunity to learn how generic characters ma}- be ascer- 

 tained, even without comparing many species. 



These new genera differ in reality in the same maimer as \'idtur, C'atluutes, 

 and Gypaetas, or as Pandion, Aquila, and Harpyia, or as Milvus, Pernis, Buteo, 

 and Circus, etc., differ one from the other. The same may be said of Chelydra, 

 and Gypochelys, of Ozotheca and Cinosternum, etc. I need not enumerate here 

 the characters of these genera, which are fully given hereafter in their proper 

 places. Moreover, any one who would competently discuss this question, should 

 examine specimens of all these species for himself, zoologically and anatomicallv, 

 when he will at least perceive that, in all our systematic works on llerpetologv. 

 the species of our Terrapins arc either placed side by side without any refer- 

 ence to their true affinities, or grouped together according to characters which 



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