400 AMERICAN TESTUDINATA. Part II. 



ish brown. The largest specimen I have seen measured twelve inches from the 

 front to the hind margin of the carapace, and ten inches across. 



This species, which is the smallest of the North American Trionychidce, extends 

 from the States of New York and Pennsylvania westwardly to the tributaries of 

 the Missouri, and the upper and middle Mississippi. I have never seen specimens 

 from the lower course of the Mississippi, nor from the Southern and South-east- 

 ern States. It is common in Lakes Erie and Ontario, (Maj. LeConte ;) in Ohio, (Dr. 

 Kirkland,) and in Indiana, (LeSueur.) Through the kindness of Prof Rich. Owen I 

 have obtained specimens from the very locality from which LeSueur described liis. 

 Dr. J. Rauch has sent me specimens from Iowa, Mr. G. Stolley from the Osage 

 River in Missouri, and Prof Sp. Baird from the Alleghany River in Pennsylvania. 

 The eggs are smaller than those of the other species of this family which I kuow. 

 They are represented (PI. 7, fig. 21) from specimens sent me by Dr. J. Rauch 

 of Burhngton, Iowa, and by Mr. Franldm Hill of Delphi, Indiana. 



II. PlatypeLtis, Fits. 



The head is short, broad, and high ; its front part is turned down steeply, 

 and makes a sharp angle with the brain-box. The sides of this part approach 

 each other gradually to the base of the proboscis, which is straight. The nos- 

 trils are terminal, and nearer together than in Amyda, crescent shaped in form 

 and vertical in position ; they are subdivided by a horizontal ridge, projecting on 

 each side of the median partition, which is wider than in Aspidonectes. The outer 

 surface of the maxillaries slants far outward from the suture with the prefrontals 

 down to the alveolar edge, thus making the mouth very broad. The alveolar 

 edge is blunt, except at the front end; it is turned down but httle at<the sides, 

 and flares out so much there that in the adult there is but Httle distinction 

 between the vertical and horizontal alveolar surfaces, and both together form one 

 very broad surface adapted to crushing ; but, at the front end, this surface is nar- 

 row and nearly vertical. There is here, as in Amyda and Aspidonectes, a large 

 opening in the skull between the intermaxillaries and the end of the vomer. 

 The lower jaw, like the upper, has a very broad alveolar surface, which also 

 continues broad back to the hind end of the maxillaries, projecting near that end 

 far over both the outer and inner surfaces of tlie jaw below, and reaching inward 

 farther even than its bwer edge. This surface is nearly flat at the symphysis, 

 but it has a deep depression near the hind end. In this genus, then, the mouth 

 is large, but short; the jaws are strong, and the alveolar surfaces broad and blunt, 

 and well fitted to crush. The shells of a Paludina and fragments of Anodontas 



