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 inframarginals 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 fipierals: 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 Emydide and of Testudinide. 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 O. borealis. 
Wieland has described and figured the ulna, the tibia, 2 metatarsals, and 1 cervical 
vertebra. Fig. 146, from Wieland, represents the femur. 
This species is most nearly related to the type of the genus, Osteopygis 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 O. emarginatus is only slightly smaller than 
the type of O. grbb:, the nuchal of the former measuring along the front 122 mm.; that of 
the latter, 127 mm. The first vertebral scute of O. emarginatus is close to 82 mm. long; that 
of O. gibbi, 110 mm. The width of the second vertebral of O. emarginatus, at the anterior 
end, is close to 75 mm.; that of O. gzbbi, about 102 mm. 
Osteopygis robustus sp. nov. 
Figs. 147-151. 
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 O. emarginatus and O. gibbi makes 
it evident that they belong to a hitherto undescribed species. The differences will appear as we 
