64 



more accurately the proper characters of family groups, 

 especially as illustrated in the order of Turtles. 



It was readily seen on examination that there were several 

 groups of genera in that order. Whenever the general form 

 was considered to be the peculiar character of a group, the whole 

 order became readily divisible into well-distinguished families, 

 and their value as natural groups was easily recognized. By 

 general form, he did not mean vague form, with its particulars 

 so eliminated as to apply to a wider group than a genus from 

 its very indefiniteness ; but a form with fixed and definite ele- 

 ments, having their origin in the disposition of the whole 

 structure, a disposition arising from the habits, manner of loco- 

 motion, &c. of the animal. 



The families thus demonstrated to exist amongst North Amer- 

 ican turtles are seven, constituting two natural groups, which are 

 distinguished by different modes of locomotion, and the resul- 

 tant general symmetry, or simplicity, or complication of structure. 

 They are therefore designated as sub-orders, those of Sea-Turtles 

 and of Emyda3. The Sea-Turtles live free in the water, and 

 move principally by means of the front limbs, after a manner 

 very much like the flying of birds ; the anterior extremity is 

 reduced to a kind of wing, and the posterior to a kind of paddle. 

 The EmydiB move principally upon the solid surface, either on 

 land or upon the bottom of the sea, and always with both pairs 

 of limbs acting in concert, as in mammals. 



Prof. Agassiz observed, that for years he had been endeavor- 

 ing to remove all the elements of arbitrary classification in the 

 study of natural history, and that he had been aiming at the dis- 

 covery of complete standards for classes, orders, families, &c. 

 Different naturalists divide the animal kingdom each into a dif- 

 ferent number of classes, and there is a great discrepancy of 

 opinion as to what the terms order, family, &c., should be 

 applied. His object was to show that the only true and proper 

 classification is that of nature, not of man. 



Dr. A. A. Gould read a letter from Mrs. M. A. Binney 

 tendering a certain portion of the library of the late Dr 

 Amos Binney, one of its former Presidents, as a deposit 

 in the library of the Society, upon the conditions given 



