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 puncte. 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 Cyclanorbis senegalensis, as figured by Siebenrock (Sitzber. Akad. Wissensch. 
Wien, xct, 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 1omm. 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 1omm. 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. 642. 
Trionyx, Leipy, Contrib. Ext. Fauna West. Terrs., 1873, p. 180, plate xvi, figs. 1, 2. 
Anostira molopinus, Corr, Paleont. Bull. No. 1, July 29, 1873, p. 4615 Proc. Amer. Philos. Soc., X11, 
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 xviil, fips O—14.— 
Hay, Bibliog. and Cat. Foss. Vert. N. A., 1902, p- 452- 
Plastomenus communis var. ii, Cope, Wheeler’s Surv. W. tooth Merid., 1877, p- 59, pl. 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. 
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