1G7 



A fourth specimen referable to Baena arenosa consists of a small portion of 

 the carapace with a large portion of the plastron, from Henry's Fork of Green 

 River, found by Dr. Carter, and presented by him to the Academy of Natural 

 Sciences of Philadelphia. This exhibits no peculiarity, excepting that the 

 scutal grooves of the plastron are more irregular in their course than in the 

 preceding specimens. The median groove of the plastron is especially tor- 

 tuous, while in the other specimens it is nearly straight. A retained portion 

 of one of the sternal bridges exhibits evidences that four scutes impressed 

 them, arranged nearly as in the first-described specimen of Baena. The sur- 

 face of the plastron is less smooth than in the previous specimen, but it does 

 not present the fretted appearance of the two ftfrmer ones. 



A fifth specimen, apparently referable to B. arenosa, consists of the anterior 

 extremity of a plastron, represented in Fig. 3, Plate XV. It was found at 

 Grizzly Buttes by Dr. Joseph K. Corson, and by him presented to the 

 Academy of Natural Sciences. It would appear from its size as if it had 

 belonged to a larger individual than the preceding specimens. It is nearly 

 flat, or in a trifling degree convex, and is smooth, or without any appearance 

 of fretting. It exhibits the four gular scute areas of unequal extent. 



Another specimen, consisting of the anterior extremity of a plastron, appar- 

 ently of a young animal of the same species, is represented in Figs. 4, 5, 

 Plate XV. The specimen was found at the junction of the Big Sandy and 

 Green Rivers, Wyoming, during Professor Hayden's exploration of 1870. 



In this specimen the sutures are visible, and the contiguous bones defined 

 The grooves defining the two pairs of gular scutes start all from the same 

 point, which is near the center of the entosternum. The entpsternal bone 

 viewed below is pyriform, but in the reverse position to that ordinarily 

 observed in emydes. Viewed above, it resembles that of the snapper, 

 (Chelydra,) or that of the sea-turtle, (Chelone.) In front it is received 

 between the episternals ; behind, it forms two lateral barbs projecting 

 obliquely outward between the episternals and the hyosternals, and a long, 

 median, pointed process extending between the hyosternals. The episternals 

 posteriorly are angular, and are there received into a notch of the hyosternals. 



From the matrix of the first-described specimen of the shell of Baena I 

 obtained a portion of the pelvis, which presents some anatomical points of 

 importance. 



