161 



flattened, and forms a continuous convexity with tlic sides. The posterior 

 extremity presents a deep emargination as in the snapper, and on each side is 

 notched likewise as in the latter. 



The plastron of Baena is emydoid in character, and in its degree of develop- 

 ment in relation with the carapace approaches that of its associate genus Bap- 

 temys. As in this, large spaces exist between the extremities of the plastron 

 and carapace, but comparatively of much less extent than in Chelydra. The 

 pedicles of the plastron are immovably conjoined with the carapace. They 

 are as wide relatively as in the emydoids, but are much longer. The two 

 extremities of the plastron are nearly alike in shape, being tongue-like and 

 feebly emarginate at the end. 



The number, arrangement, and general form of the corneous scutes of the 

 carapace appear to have been the same as in Emys and Chelydra. The plastron 

 exhibits two pairs of gular scute areas, which, together with the other scute 

 areas, made seven pairs to the plastron. In addition to these the pedicles 

 exhibit a row of scute areas between the former and the marginal scute areas 

 of the carapace, as in the sea-turtle, the snapper, Dermatemys, and Baptemys. 



A feature which may be regarded as a character of Baena is the obliteration 

 • of the sutures, and the shell at maturity has the bones so co-ossitied that their 

 original boundaries cannot be traced. 



The true ribs or costal arclies, connate with the costal plates, are remark- 

 ably prominent in Baena, and the costal capitula are well developed. In 

 several specimens, in which portions of the carapace. arc broken away, the 

 mass of rock within exhibits deep concave grooves indicating the former 

 position of the rib-arches. 



The sustaining columns of the carapace, springing as processes from the 

 hyosternal and hyposternal bones of the plastron, are of great comparative 

 breadth, and subdivide the interior of the shell into three compartments as in 

 tlie Batagur, a genus of fresh-water turtles now living in India. 



Baena arenosa. 



The species thus named was originally founded on a specimen consisting 

 of a nearly complete turtle-shell discovered at the junction of the Big Sandy 

 and Green Rivers, Wyoming, during Professor Hayden's exploration of 187U. 

 The specimen is represented in Figs. 1, 2, Plate XIII. 



The shell, besides appearing to be in some degree crushed downward or 

 21 G 



