244 AMERICAN TESTUDINATA. Part II. 



tion from the rest of the order, in the farther subdivision of which we find, 

 however, the greatest discrepancy among modern herpetologists. But, whether we 

 subdivide the digitated Chelonians of Oppel and Merrem into two, or three, or 

 more natural groups, the question at once arises, how these groups shall be called, 

 whether they are sections, sub-orders, families, or tribes, names which in the chaos 

 now prevailing in nomenclature might seem equally applicable to all and any of 

 them, or whether nature points out a real difference between them. Let us 

 consider, in the first place, the more extensive of these groups, such as they are 

 admitted by Oppel under the names of Chelonii and Amyd.e, and by Merrem and 

 Bell under the names of Pinnata and Digitata. What do they indicate ? A differ- 

 ence in the mode of locomotion, that is to say, a structural difference, and that 

 difference is of such a kind that, whether consciously or unconsciously, all authors 

 have regarded those Turtles which have pinnate limbs as inferior to those in which 

 the fingers are distinct. We find, at least, that in all works in which the animal 

 kingdom is arranged in a descending order, the digitated Testudinata are mentioned 

 first, the pinnate last, and where these are subdivided, as they have been by 

 Ritgen, Wagler, Dumeril and Bibron, and Canino, those with club feet are placed 

 above those with webbed fingers. Their intention is therefore evident, to mark 

 the respective rank of the Testudinata in these subdivisions of the order, a grada- 

 tion which is, however, not founded upon differences in the whole structure, but 

 only on such as are prominently marked in some parts of the body. In as far 

 then as this is correct, these divisions all partake of the character of orders; 

 they are akin to what we have called orders, inasmuch as orders are founded 

 upon the gradation or complication of structure, but they are not real orders, 

 inasmuch as that gradation does not extend to all the organic systems of their 

 structure. At least, it is neither so extensive as to aftbrd a means of com- 

 parison of any of them singly with any other order of the class, without involv- 

 ing the enumeration of characters common to all ; nor is the element of form, 

 which is so important in the characteristics of families, introduced distinctly in any 

 of these minor groups. 



We can, therefore, consider these divisions only as sub-orders; and the precision 

 with which their gradation can be pointed out from the Thalassites through the Pota- 

 mides and Elodites to the Chersites leaves no doubt in my mind that, whether 

 two general groups are to be adopted under the head of Testudinata, as Oppel, 

 Merrem, and Bell recognize, or three, as Ritgen and Wagler admit, or three com- 

 bined in the manner in which Canino has them, or four, as Dumeril and Bibron 

 have them, these divisions must be considered as sub-orders, since they express 

 a gradation within the order, or, in other words, are founded, under certain limi- 

 tations, upon characters of the same kind as those on which the whole order is 



