T R I O N Y X M U T I C U S . 19 



some of them common to the T. ferox, and others are not always present, still 

 he gives two characters which always exist. 



1. The total absence of spines or tubercles; and this is by no means the result 

 of age, for they are never seen in large or small, young or old; whereas the 

 spines always exist in the Trionyx ferox, even on those not over three inches in 

 extent, as I have had abundant occasion to observe. 



2. The difference of the nostrils, as above described, which is equally constant. 

 And to these others might be added, as, the difference in size, difference of 

 geographical distribution, having never been found to the east of the Alleghany 

 range of mountains, &c. 



I have never yet had an opportunity of examining thoroughly this animal, as 

 might be desired, to study its internal structure; yet Troost writes me, that its 

 bony system differs in many remarkable points from that of the Trionyx ferox. 



These are the only species of Trionyx that I am as yet prepared to admit into 

 the catalogue of reptiles inhabiting the United States. The Trionyx ocellatus 

 of Lesueur I consider only as the young of the Trionyx ferox, having had frequent 

 opportunities of observing them. 



