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 kempt has a perfectly solid carapace. 



Therefore, until better tharacters have been proposed for the separation of Osteopygis 

 and Propleura, the present writer prefers to employ only the former name. 



Osteoygis emarginatus Cope. 



Teit-fi 



134-141. 



Osteopygis emarginatus, COPE, Proc. Acad. Nat. Sci., 1868, p. 147 (nom. nucl.); Cook's Geol. New Jersey, 

 1868 (1869), p. 735 (nom. nud.); Amer. Naturalist, in, 1869, p. 89; Ext. Batrach., Reptilia, Aves 

 N. A., 1869, pp. 135, 136, 235, plate vii, fig. 3; Vert. Cret. Form. West, 1875, P- 2 59- HAY, 

 Bibliog. and Cat. Foss. Vert. N. A., 1902, p. 441. 



Osteopygis platylomus, COPE, Ext. Batrach., etc., p. 134, fig. 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 



FIG. 134. Osteopygis emarginatus. Nuchal, right first peripheral, and portions of first 

 costals. Xi No. 1485 A. M. N. H. 



c.p. i, First costal bone; nu.p, nuchal bone; nu.s, nuchal scute; per.i, 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 y. 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 is the same one 

 he called the tenth of the left side. On the bone there has at some time been written, probably 



