1G5 



deficient. In consequence of its absence, a modification of the outlines pf the 

 contiguous ones resulted. The posterior groove of the axillary scute, and the 

 anterior groove of the area corresponding with the second submarginal scute 

 in the first specimen, instead of being transverse are oblique aud join each 

 other at an angle externally. The posterior two scutal areas also differ from 

 those of the first specimen in being separated by a groove directed obliquely 

 outward and backward instead of nearly transversely. 



The surface of the plastron exhibits the same minutely fretted appearance 

 as in the former specimen. 



In the perfect condition the two specimens of Baena which have been de- 

 scribed differed but little in size. The length of the carapace in a straight line 

 has approximated 13 inches, the breadth 9 or 10 inches. The length of the plas- 

 tron is 11 inches; its breadth to its conjunction with the carapace about 8 inches. 



A third and less perfect specimen of the shell of Baena arenosa, consisting 

 of the central portion of the carapace and nearly the corresponding portion 

 with the anterior extremity of the plastron, was found by Dr. Carter on 

 Henry's Fork of Green River, and presented by him to the Academy of 

 Natural Sciences. 



This specimen had about the same size as the previous ones, and like them 

 has all the bones completely co-ossified. The median ridge of the carapace is 

 more distinct than in the other specimens, and its divisions appear more or 

 less distinctly to mark the position of the vertebral plates, while the lateral 

 diverging prominences also appear to mark the sides of these plates. 



The intermediate vertebral scute areas are intermediate in proportions to 

 those of the former specimens. 



The surface of the plastron is smooth and exhibits no trace of the minutely 

 fretted condition observed in the former specimens. The grooves defining 

 the sternal scute impressions, the median groove as well the more transverse 

 ones, are less regular in their course than in the other specimens. 



The anterior extremity of the plastron, represented in Fig. 2, Plate XV, is 

 flat, and exhibits the second pair of gular scute areas larger than in the former 

 specimen in which they exist, while their more tortuous back groove starts 

 from the median groove a half inch behind that in front. The rounded bor- 

 der is more prominent in the position of the gular scute impressions than in 

 the former specimen. 



A small part of the sternal bridges retained in the specimen shows a por- 



