163 



behind, extend upon the posterior half of the breadth of the sternal bridges. 

 Their posterior groove is directed obliquely outward and backward to the 

 bottom of the inguinal fossae. 



The femoral are considerably lai'ger than the costal scute impressions, and 

 defined from them by a sigmoid groove. 



The bridges of the plastron present a row of four large scutal areas inter- 

 vening between the pectoral and abdominal scute areas internally, and the 

 marginal-scute areas of the carapace externally. The first and last of these 

 may be regarded as homologues of the comparatively small axillary and ingui- 

 nal scute areas of Emydes; the intermediate ones are superadded. 



The axillary scute area, partially broken away in the specimen, appears to 

 have had four borders, of which the anterior formed the outer boundary of 

 the axilla, and the internal joined the pectoral scute area. 



The second submarginal scute area, the smallest of the series, is quadrate, 

 and internally joins the pectoral scute area. The succeeding submarginal 

 area, larger than those in advance, is pentagonal, with the two shorter sides 

 forming a projecting angle joining the pectoral and abdominal areas. 



The inguinal scute area, larger than the others, has four borders, of which 

 the internal joins the abdominal area, and the posterior bounds the greater 

 part of the bottom of the inguinal space. 



The surface of the carapace is somewhat irregular ; that of the plastron is 

 more regularly and minutely roughened or fretted in appearance. 



A second nearly complete specimen of a shell of Baena was discovered by 

 Dr. J. Van A. Carter at Church Buttes, on Black's Fork of Green River, three 

 miles north of Fort Bridger, and was obligingly sent to the writer as a gift. 

 The shell, like the former one, is considerably crushed, so as to render an 

 exact determination of its original form uncertain. It approximated the other 

 specimen both in shape and size, and, like it, has all the bones so completely 

 co-ossified that their limits are obliterated. 



This second specimen presents several differences from the former one, 

 which led to its having been considered as pertaining to another species, to 

 which the name of B. affinis was given. Additional specimens since obtahied 

 and exhibiting other variations have led to viewing all of them as belonging 

 to a single species. 



The carapace measures 13 inches in length following the curvature. Its 

 anterior portion, preserved in the specimen on one side, has a rather obtuse 

 border, and is not recurved. In front it is prominent, as far as seen in the 



