88 



FOSSIL TURTLES OF NORTH AMERICA. 



the intercostal sutures are a few of the grooves described by Cope. Fortunately the sutures 

 between the bones are yet open, so that the whole structure can be observed. The most 

 striking feature of the carapace is the presence of two bones in the region usually occupied by 

 the nuchal, a small anterior and a large posterior. The anterior bone (fig. 76, nu.f), here regarded 

 as the true nuchal, has awidth of 52 mm. and a length, fore and aft, of 30 mm. The other bone, 

 the preneural (fig. 76, pren), is 75 mm. wide and 38 mm. long. The first neural is pyriform, 

 the others hexagonal, with the wider end forward. 



The first three peripheral bones are each 42 mm. high. 

 Those over the bridges have a height of about 65 mm. 

 There are 6, instead of 5, vertebral scutes, the areas usually 

 covered by the first being transversely divided. The dimensions 

 of the neurals and vertebrals are shown in the table. 



The nuchal scute is small and was probably not divided 

 along the midline. It is 24 mm. wide and 10 mm. fore and 

 aft. The first marginal is small and triangular. The second 

 has a length of 25 mm. along the free border and a height of 16 

 mm. The third is not so high. Those marginals over the 

 bridge rise above the borders of the costal bones and have 

 a height of approximately 70 mm. 

 A little of the hinder border of the plastron (fig. 77) is broken away, but the total length 

 was very close to 415 mm. In general it resembles the plastron of species ofBaena. The length 

 of the anterior lobe is 113 mm.; its width at the base, 160 mm.; at the outer ends of the gulo- 

 humeral sulci, 85 mm. The entoplastron is 65 mm. long and 45 mm. wide. The symphysis of 



the epiplastra is only 14 mm. long. From 

 the entoplastron the hyoepiplastral sutures 

 run outward and backward. The bridge 

 has a width of 180 mm. The mesoplastra 

 join at the midline for a distance of 20 mm., 

 the left one being somewhat the wider. 

 They expand outward to awidth of 105 mm. 

 The length of the hinder lobe was 

 originally about 105 mm. Its basal width is 

 175 mm.; at the hypoxiphiplastral suture, 

 145 mm.; at the femoro-anal sulci, 120 

 mm. The thickness of the center of the 

 anterior lobe is n mm. Between the 

 axillary buttresses, on the upper surface, 

 runs a broad ridge which thickens the bone 

 to 15 mm. A similar ridge crosses from 

 one inguinal buttress to the other. From 

 the latter buttresses a ridge runs backward 

 near each free border of the hinderlobe,and 

 thru these the thickness is 17 mm. The 

 central part of the hinder lobe is concave. 

 The skull (plate 21, figs. 3, 4; plate 23, fig. i; text-figs. 78-81) of this specimen is nearly 

 complete, lacking only a part of the left maxilla, and the premaxillae. At the time the writer 

 publisht his figures of this skull, he had not yet discovered the differences between this 

 specimen and that numbered 5962, described here as Chisternon undatum. In order to allow 

 comparisons the measurements of the two skulls are given in the table on p. 89. 



There is a difference of only 5 mm. in the lengths of the skulls. There is a difference of this 

 same amount in the widths of the maxillae below the orbits, a difference of 8 mm. in the widths 

 of the skulls at the quadrates, a difference of 6.5 mm. in the distances from the orbit to the 

 tympanic cavity. 



The skull is short, broad behind, wedge-shaped in front. The temporal region is broadly 

 rooft over and the squamosal comes into contact with the parietal. 



FIG. 77- Chisternon hebraicum. Plastron. Xj. No. 

 5961 A. M. N. H. Shows bones and scute areas. 



