THALASSEMYDID&, 129 
The possession of conical rib-pits on the part of Wieland’s Propleura borealis, if a good 
generic character, removes it from Propleura, for the type of the latter, P. sopita, has the pits 
in the hinder peripherals all flat. This statement is true as regards Leidy’s type of his Chelone 
sopita and of Cope’s specimen, now regarded as belonging to Osteopygis borealis. 
There remains therefore only the presence of the costo-peripheral fontanels to separate 
Propleura from Osteopygis. This is one of those characters which can not be sharply defined 
and which may be expected to exhibit in closely related species all gradations. We can not 
be sure that at any time a species may not be found in which a number of the lateral peripherals 
are joined suturally with the costals, while others are free. Indeed, we can not be certain that 
in some of the described species of Propleura some of the lateral peripherals did not become 
sutured to the contiguous costals. An aged Colpochelys kempi has a perfectly solid carapace. 
Therefore, until better characters have been proposed for the separation of Osteopygis 
and Propleura, the present writer prefers to employ only the former name. 
Osteoygis emarginatus Cope. 
Text-figs. 134-141. 
Osteopygis emarginatus, Cope, Proc. Acad. Nat. Sci., 1868, p. 147 (nom. nud.); Cook’s Geol. New Jersey, 
1868 (1869), p. 735 (nom. nud.); Amer. Naturalist, 111, 1869, p. 89; Ext. Batrach., Reptilia, Aves 
N. A., 1869, pp- 135, 136, 235, plate vii, fig. 3; Vert. Cret. Form. West, 1875, p. 259.—Hay, 
Bibliog. and Cat. Foss. Vert. N. A., 1902, p. 441. 
Osteopygis platylomus, Cope, Ext. Batrach., etc., p. 134, fg. 39 in part. 
The two specimens described by Cope under this name are in the American Museum of 
Natural History. Both had been discovered in the upper bed of greensand of the Upper 
Cretaceous, at Barnesboro, Gloucester County, New Jersey. The bones figured by Cope 
betes | 
We = 
Fic. 134.—Osteopygts emarginatus. Nuchal, right first peripheral, and portions of first 
costals. 3. No. 1485 A. M.N.H. 
¢. p. 1, First costal bone; nu.p, nuchal bone; nu.s, nuchal scute; per. 1, first peripheral. 
belong to the second individual described by him. This is in the American Museum and bears 
the number 1485. 
There is, however, some doubt attached to the peripheral which furnisht Professor Cope s 
figure 3c. In his explanation of the figure, Cope says that it is the tenth of the left side. 
In reality, it is the eighth. He states that the eleventh peripheral of the right side is present, but 
it is not in the collection. It seems probable that the one he called the eleventh 1s the same one 
he called the tenth of the left side. On the bone there has at some time been written, probably 
9 
