72 



FOSSIL TURTLES OF NORTH AMERICA. 



38 mm. long and 15 mm. high. The seventh, lying below the hinder half of the second costal, is 

 56 mm. long and it rises about 36 mm. above the free border of the shell. On account of the 

 obtuse border over the bridge the elevation of the lateral scutes is difficult to estimate. 



The plastron (fig. 53) is 320 mm. long. The anterior lobe is 92 mm. long, 112 mm. wide 

 at the base, and 80 mm. wide at the gulo-humeral sulci. The bridge has a width of 138 mm., 60 

 per cent, of the length of that part of the plastron behind the axillary notches. The hinder lobe 

 is 92 mm. long, 127 mm. wide at the base, and 92 mm. at the ends of the femoro-anal sulci. 

 The hinder border is slightly excavated. 



The mesoplastra are solidly co-ossified with the contiguous bones, but some traces are 

 found of the sutures. The bones appear to hrfve been about 15 mm. wide at the midline. 



The forms of the various plastral scutes are shown in the figure. The course of the median 

 sulcus is very tortuous and there are some irregularities in the others. The axillary region is 

 damaged on both sides, but appearances indicate that there were 3 left inframarginals, the 



FlGS. 52 AND 53. Ba'ena sima. Type. Xj. Showing the form of carapace 

 and plastron and the scute areas. 



52. Carapace. 



53. Plastron. 



pectoral scute apparently having extended out to the marginals. There is a large inguinal 

 inframarginal and another in front of it. There was doubtless an axillary scute, but the bones 

 are missing which supported it. On the right side there were 4 inframarginals. 



The skull of this species (plate 13, figs. 1, 2; plate 14, fig. 4) is remarkable for its breadth 

 and shortness. The premaxillary region is missing and likewise the condyle of the basioc- 

 cipital; but the length from one to the other was very close to 64 mm. The breadth across the 

 quadrates is 71 mm. From the quadrates the outline of the skull contracts rapidly to below 

 the front of the orbits, where there is a sudden constriction. From this the outline contracts 

 slowly, then rounds into the broad snout. The upper surface is convex. All the bones are 

 solidly co-ossified, and no sutures are to be traced. 



The temporal fossae are rooft over extensively, so that between the end of the short 

 supraoccipital and the postero-lateral angles there is on each side only a shallow sinus. The 

 interorbital space is 26 mm. wide. The orbits have their greatest diameter, 17 mm. directed per- 



