366 AMERICAN TESTUDINATA. Part II. 



are all herbivorous, inofiensive, and shy. The Trionychidaj, on the contrary, which 

 Hve upon fresh-water shells and the larvae of aquatic insects, are quick in their 

 motions, and bite about them Uke Snakes ; while the Chelydroidae, which live upon 

 a large and active prey, are as ferocious as the wildest carnivorous beasts. The 

 Cinosternoidse, though also carnivorous, are rather active than fierce; the omniv- 

 orous Emydoidae are more timid and inoffensive, and exhibit greater diversity in 

 their mode of life; while the herbivorous Testudinuia have the grave and con- 

 fiding disposition of many of the Ruminants, though, owing to their slow motion, 

 they have to trust solely to the strength of their covering for defence. But 

 this coincidence, between the natural limits of families and the mode of life of 

 their representatives, cannot be considered as a general rule obtaining throughout 

 the animal kingdom, for among Fishes we find the most diversified habits in the 

 same family. Among the Salmonidce, as hmited by J. MiiUer, who first recognized 

 the natural boundaries of that family, there are voracious species, provided with 

 strong, pointed teeth, and feeding exclusively upon hving prey, such as the true 

 Salmons and others which are entirely destitute of teeth and live upon decaying 

 organic substances, such as the Coregonus. And yet these Fishes exhibit none of 

 those striking differences which we are accustomed to consider as characteristic in 

 the structure of carnivorous and herbivorous animals. Neither their alimentary canal, 

 nor the large glands, nor the appendices pylorici connected with it, exhibit marked 

 differences. This shows how cautious we ought to be in aj)plying the mode of 

 life of any animals as a test of their affinity. 



