THALASSEMYDID&. 149 
have been taken from the plastron of one of the specimens described by him as O. emar ginatus. 
Remarks on this specimen are made under the last-named species. In Cope’s figure of the 
plastron the hyoplastron on the left side of the drawing is placed too horizontally. T tie anterior 
outer angle ought to be directed strongly forward. This species resembles O. borealis. For 
differences see under the latter species. 
Osteopygis sopitus Leidy. 
Figs. 181-184. 
Chelone sopita, Leipy, Smithson. Contrib. Knowl., xtv, 1865, pp. 104, 119.—Maack, Paleontographica, 
xvi, 1869, pp. 238, 283. 
Osteopygis sopitus, Hay, Pibien: and Cat. Foss. Vert. N. A., 1902, p. 441 (in part). 
The type specimen of the present species has not hitherto been figured. It belongs to the 
New Jersey State collection and is at Rutgers College, New Brunswick, New Jersey, where 
the writer has examined it. This type consisted of 4 peripherals, but Leidy was uncertain 
whether or not they belonged to one individual. These bones had been obtained in the 
Cretaceous greensand at Tinton Falls, Monmouth County, New Jersey, probably in the upper 
bed. Other specimens, which were mentioned by Leidy in his description of this species and 
figured, were afterwards referred by Cope to Lytoloma angusta, and probably correctly so. 
182a. 
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184. 
Fics. 181-184.—Osteopygts sopitus. Peripheral of type. 
181. Seventh? peripheral, with section. 
182. Hinder peripheral, with section (182a). The interrupted line of the 
section indicates the depth of the pit. 
183. Hinder peripheral. 
9. 
184. Section of a peripheral. 
Other specimens were referred by Cope to Leidy’s species. One of these had been 
secured at Harrisonville, Salem County, New Jersey, in a sort of limestone. This specimen 1s 
now in the American Museum of Natural History and has the number 2361. Almost certainly 
it is not a species of Oste eopygis, and it has in the present work been referred provisionally 
to Rhetechelys platyops (Cope). 
The four peripherals of the type belonged behind the bridges. Figures taken from three 
of these are here presented. Fig. 181 represents in outline one which is regarded as being the 
right seventh. It is 115 mm. long, 59 mm. wide near the anterior end, 20 mm. thick at this end, 
and 12 mm. at the posterior end. There are 3 faces—an upper, a lower, and an inner, or 
visceral. The pit for the rib is nearer what is regarded as the hinder end and is somewhat 
flattened in section. Above the figure is a section taken at the anterior end of the bone. Another 
peripheral (fig. 182) is about 87 mm. long, 82 mm. wide, 18 mm. thick at one end, 14 mm. at 
the other. In the visceral face is a pit for the end of a rib. Each diameter of the pit at its 
opening is g mm. The upper face is quite concave from the acute free border to the costal 
border. Near the figure is a section (1822) taken at the thicker end of this peripheral, which 
represents the diameter and depth of the rib-pit. Another peripheral, probably a ninth or 
tenth, has the costal border broken away. The rib-pit is flattened. Figure 183 is a section of 
this bone. Its greatest thickness is 24 mm. Fig. 184 is a section taken alshe the transverse 
sulcus of a fragment representing about one- -half of a peripheral. The upper and lower faces 
