86 



FOSSIL TURTLES OF NORTH AMERICA. 



greatest width, 387 mm. The outlines of many of the neural bones are determinable. On the 

 front of the carapace, however, the indications are obscure. The vertebral scutes are a little 

 longer than wide. The scutes on the front of the carapace are unsymmetrical. On the left 

 side there is a supernumerary costal, but not on the right side. The anterior vertebral is not 

 transversely divided as it is in the other specimens. Over the bridges the marginal scutes are 

 not more than 45 mm. high. The anterior lobe of the plastron is missing. On the left bridge 

 there are only three inframarginal scutes. 



No. 5974 was collected in 1903 near the mouth of Cottonwood Creek, in the level called B 2 . 

 It has a length of 490 mm. along the midline, and a maximum width of 425 mm. The rear of 

 the carapace is scallopt. Most of the sutures are indistinct, but the small nuchal and the 

 large preneural are plainly separated. The former is 38 mm. long and 46 mm. wide; the latter, 

 45 mm. long and 72 mm. wide. The first vertebral scute is transversely divided, so that there 

 are present really 6 vertebrals. On each side of the two anterior ones is a supernumerary costal, 

 and an extra scute has been cut ofFfrom the first vertebral and the right supernumerary costal. 

 The marginals over the bridges appear not to run more than 50 mm. above the borders of the 

 shell. The plastron is 440 mm. long. The entoplastron has a length of 80 mm. and a width 

 of about 45 mm. The mesoplastral sutures are not wholly distinct, but these bones appear 

 to have come to a point at the midline. The anterior lobe is 120 mm. long; 150 mm. wide at 

 the base; 93 mm. wide at the gulo-humeral sulci. The bridge is 205 mm. wide. The hinder 

 lobe has a length of 125 mm.; a width of 155 mm. at the base, 122 mm. at the femoro-anal 

 sulci. On each bridge are 4 inframarginal scutes. The gulars meet each other for a dis- 

 tance ot 13 mm. at the midline. 



Vertebral. 



Length. Width. 



IV v ^ \js 74 . 



Figs. 73-75. Chisternon undatum. Skull of No. 5962 A. M. N. H. xi. 



73. Skull seen from above. 74. Skull seen from below. 75. Right half and tip of lower jaw. 



No. 5959 (fig. 72) was obtained at Grizzly Buttes, Wyoming, in 1903. The axial length of 

 the carapace is 455 mm.; its width, 400 mm. As in No. 3932, there is a broad depression along 

 the midline of the carapace. There is a distinct nuchal bone, followed by a larger preneural. 

 There are 6 vertebral scutes, whose dimensions are given in the accompanying table. 



There is a small supernumerary costal scute on each side of 

 the first vertebral scute and another on each side of the second 

 (fig. 72). The border of the shell over the right bridge is crusht, 

 but the costo-marginal sulci appear to have run not more than 

 60 mm. above the border of the shell. The entoplastron is 80 

 mm. long and about 48 mm. wide. On the right bridge are five 

 inframarginals. The left bridge is missing. 



No. 5962 was collected at Grizzly Buttes, in 1903. It was 

 lying close to No. 5961, a specimen ot C. hebraicum. The cara- 

 pace is much crusht laterally and diagonally. The specimen is 

 valuable because it furnishes the skull. The carapace was at least 460 mm. long. So far as 

 can be determined, the costo-marginal sulci pursued their courses above the bridges at a moder- 

 ate height. There are 6 vertebral scutes and a pair of supernumerary costals in front. There 

 are traces of the suture between the nuchal and the preneural. 



Most ot the dimensions of the skull (figs. jt 74) are presented on page 89. It differs from 

 that of (7. hebraicum especially in the broader triturating surfaces of the maxillae and the broader 



