PLASTOMENID^. 481 



The pits are shallow and in many portions of the carapace, especially near the midline and 

 on the rear, they are obsolete. Many of them form what Cope has designated punctae. They 

 cover the nuchal, the outer halves of the anterior costals, and distal thirds of hinder costals. 



A considerable portion of the plastron (fig. 641) is preserved, but it is fragmentary and, 

 in many cases, there is contact between the fragments present. It is believed, however, 

 that the restoration presented by fig. 641 is not far from correct. The specimen has furnisht 

 the entoplastron, a part not hitherto known in the genus. 



The length of the plastron, from the front of the entoplastron to the hinder end of the 

 xiphiplastrals, is about 245 mm.; the width about 275 mm. Evidently there were no fontanels 

 in the midline, except a short and wide one just behind the entoplastron. The latter bone is 

 more like that of Cyclanorbi 's senegalensis, as figured by Siebenrock (Sitzber. Akad. Wissensch. 

 Wien, xci, 1902, p. 34), than like that of any other living species. The lateral branches of the 

 bone made an obtuse angle with each other. The original bones are covered with a thick 

 callosity and this has filled up the angle between them. The bone measures 38 mm. on the 

 midline, and is from 6 mm. to 8 mm. thick. 



The hyoplastra meet along the midline a distance of 50 mm.; the hypoplastra, a distance 

 of about 75 mm. The hinder sutural border of the hypoplastron is not present, and the xiphi- 

 plastron ought possibly to have been removed somewhat further backward, but certainly not 

 much further. The hyoplastra were flat for a distance of about 60 mm. on each side of the 

 midline; then they have sloped upward and outward. Where the slope begins, the bone is 

 about 12 mm. thick. The outer ends are considerably thinner. The outer end of the hypo- 

 plastron is 13 mm. thick, and terminates in 2 processes. The inguinal notch was abrupt. 



The hinder portion of the hypoplastron which is shown in the figure preserves the sutural 

 border which joined the bone of the opposite side. It shows therefore the width of that part of 

 the hinder lobe. This was close to 125 mm. The hypoplastron had a thickness of about 12 mm. 

 at the inner border, but thinned toward the free border. 



The median and anterior sutural borders of the xiphiplastron have not been preserved, 

 but the bone, both mesially and anteriorly, evidently approaches these sutures closely. The 

 outer, or free, border of the hinder lobe was quite certainly concave at the hypoxiphiplastral 

 suture and convex both in front and behind it. The hinder half of the xiphiplastron has a 

 thickness near the mesial border of 6 mm. ; near the free border, 4 mm. The hinder border of 

 the lobe was probably slightly excavated. 



The whole lower surface of the plastron, except possibly the epiplastra, which are not 

 known, is sculptured into a network of ridges, which inclose pits of varying sizes and depths. 

 On the entoplastron the pits are irregularly arranged and shallow, and there are 5 or 6 of them 

 in a line 10 mm. long. The median half of the hyoplastron is similarly ornamented, altho 

 toward the suture with the hypoplastron the pits become obsolete. The outer extremity of 

 the hypoplastron is furnisht with large pits, three or four in a line of 10 mm. That portion of 

 this bone which enters into the hinder lobe has the pits arranged in regular rows which run 

 parallel with the free border of the lobe. Four rows of pits occupy a distance of 10 mm. The 

 xiphiplastra are similarly ornamented, but the pits become somewhat smaller posteriorly and 

 the rows less regular. This specimen was collected in the western portion of Grizzly Buttes. 

 Cope states that two of his specimens came from Cottonwood Creek. 



Plastomenus molopinus Cope. 

 Plate 85, fig. 3; text-fig. 641. 



Trionyx, LEIDY, Contrib. Ext. Fauna West. Terrs., 1873, P- I ^> p' ate xv '> fig 8 - 1 > 2 - 



Anostira molopinus, COPE, Palaeont. Bull. No. I, July 29, 1873, p. 461; Proc. Amer. Philos. Soc., XII, 



1873, p. 461. 

 Plastomenus molopinus, COPE, 6th Ann. Rept. U. S. Geol. Surv. Terrs., 1873, p. 6 20; Proc. Acad. Nat. 



Sci. Phila. 1873, p. 279; Vert. Tert. Form. West, 1884, pp. 123, 125, plate xviii, figs. 9-14. 



HAY, Bibliog. and Cat. Foss. Vert. N. A., 1902, p. 452. 

 Plastomenus communis var. ii, COPE, Wheeler's Surv. W. looth Merid., 1877, p. 50, pi. xxv, figs. 5, 6. 



Professor Cope stated that he possest remains of 8 individuals of this species from the 

 Bridger beds of Wyoming. The specimens figured by him in his Vertebrata of the Tertiary 

 Formations of the West belonged to one individual, and consist wholly of fragmentary costal 

 plates. They are now in the American Museum of Natural History and have the number 6072. 



3 1 



