134 



FOSSIL TURTLES OF NORTH AMERICA. 



Relatively to the carapace the plastron (plate 27, fig. 2; text-fig. 144) is smaller than in 

 Caretta caretta. Nevertheless, the connection between the borders of the plastron and the 

 peripherals is more extensive than in the genus just mentioned, extending from the second to 

 the eighth peripherals. The outer anterior prolongation of the hyoplastron reaches forward 

 as far as does the anterior lobe, and the outer posterior prolongation of the hypoplastron 

 extends backward nearly as far as does the hinder lobe. The hyoplastron sends a process into 

 the second peripheral, and the hypoplastron has its hinder prolongation inserted in an excava- 

 tion of the seventh and eighth peripherals. In the fourth and sixth peripherals are small 

 pits for digitations of the plastral bones. The median longitudinal suture is a coarse one. 

 There is a median fontanel at the crossing of the hyohypoplastral suture and the median 

 longitudinal. On each side, at the ends of the hyohypoplastral suture, is another fontanel. 

 A fourth is found on the median line just in front of the xiphiplastra. 



The epiplastra are narrow bones which have a length of about 85 mm. and a width of 

 15 mm. The entoplastron is only in part preserved. It appears to have been 85 mm. long 

 and 59 mm. wide. 



The least width across the bridges is 114 mm. The hinder lobe is much reduced, leaving 

 free play for the hinder limbs. The xiphiplastra are 185 mm. long and 55 mm. wide. 



The sulci of the plastron are very obscure, but Wieland appears to have mapt them 

 correctly. There were quite certainly inframargmals on the outer ends of the bridges. The 

 sulcus between the gular and the humeral scutes has not been observed; nor that between the 

 humeral and the pectoral. Wieland calls the pectoral scutes the humerals; the abdominals, 

 the pectorals; the femorals, the ventrals; the anals, the femorals. The abdominals have a 

 width, at the midline, of about 65 mm.; the femorals, a width of 78 mm.; the anals, a width 

 of nearly 150 mm. 



Wieland has figured the humerus (fig. 145). The total length is 145 mm.; the short 

 diameter of the flattened shaft, 18 mm.; the long diameter, 21 mm. It resembles the humerus 

 of Chelydra. The angle between the planes of the ulnar and radial crests is obtuse. The 

 distal end of the bone is grooved, as in some species of Emydidce and of Testudinidce. The 

 ectepicondylar passage is a deep perforation. The femur has a length of 150 mm., therefore is 

 longer than the humerus. It resembles that of Chelydra, except that the distal end is grooved. 

 In this respect too it differs from the femur of 0. borealts. 



Wieland has described and figured the ulna, the tibia, 2 metatarsals, and I cervical 

 vertebra. Fig. 146, from Wieland, represents the femur. 



This species is most nearly related to the type of the genus, Osteopygts emarginatus 

 Cope. The latter differs in having the posterior peripherals emarginated on the free borders 

 at the end of the intermarginal sulci, in not having the upper borders notcht so as to expose 

 the end of the rib, in having a shorter first vertebral scute, and apparently in having narrower 

 second and third vertebral scutes. The type of 0. emarginatus is only slightly smaller than 

 the type of 0. gibbi, the nuchal of the former measuring along the front 122 mm.; that of 

 the latter, 127 mm. The first vertebral scute of 0. emarginatus is close to 82 mm. long; that 

 of 0. gibbi, no mm. The width of the second vertebral of O. emarginatus, at the anterior 

 end, is close to 75 mm.; that of O. gibbi, about 102 mm. 



Osteopygis robustus sp. nov. 

 Figs. i47->5'- 



In the American Museum of Natural History is a lot of bones which is accompanied by a 

 label written by Professor Cope, stating that they were found at Birmingham, New Jersey, 

 that he regarded them as belonging to Osteopygis emarginatus, and that he received them 

 November 13, 1870. Those bones which can be safely regarded as belonging to one individual 

 are the nuchal, the first and second peripherals of both sides, the tenth and eleventh peripherals 

 of both sides, the fourth costals of both sides, the left fifth, the left seventh and the eighth, and 

 the proximal end of the right eighth. There are also fragments of other costals of unde- 

 termined position. To this specimen is given the number 2360. 



A comparison of these bones with those of the types of 0. emarginatus and O. gibbi makes 

 it evident that they belong to a hitherto undescribed species. The differences will appear as we 



