62 SYSTEMATIC PALEONTOLOGY 



responds in all essential particulars. In size and general features it 

 apparently resembles most nearly the brachium of the Cinereous Petrel 

 {Pufjimis cinercus Gmelin), of the Pacific coast, but there are some 

 points of difference between them which clearly imply that the species 

 are distinct. The flat apophysis on the outer edge of the distal ex- 

 tremity is in the fossil specimen more pointed; the impression, on the 

 lower surface, of the anterior brachial muscle is deeper, and its outline 

 more sharply defined, which is also the case with the small epicondylar 

 depressions for the attachment of the muscles of the forearm. The 

 bone indicates, moreover, a somewhat smaller bird. 



" The distal half of the right ulna, which was found with the hum- 

 erus, apparently belonged to a bird of the same species, although its 

 size would seem to indicate that it pertained to a smaller individual." 

 Marsh, 1870. 



Occurrence. — Chesapeake Group. Maryland. 



Collection. — Philadelphia Academy of Natural Sciences. 



Class REPTILIA. 



Order CHELONIA. 



Suborder TRIONYCHIA. 



Genus TRIONYX Geoffrey. 



Trionyx cellulosus Cope. 



Trionyx celluloxus Cope, 1867, Proc. Acad. Nat. Sci. Pbila., vol. xix, p. 142. 



Description. — Known from a small part of the carapace. " The sur- 

 face is marked by numerous closely placed pits, which are remarkably 

 deep, producing the vesicular appearance of scoria. The resemblance 

 is heightened by the irregular size of the pits. Edges of the septa 

 rounded. The fragments are unusually thick, indicating species of large 

 size. 



Width of free portion of rib at origin 7.5 lines. 



Depth of portion of carapace 4.33 lines. 



Cope, 1867. 

 Occurrence. — Calvert Formation. Charles county near the Patux- 

 ent river. 



Collection.— FormeYly in the Philadelphia Academy of Natural 

 Sciences. 



