146 



KOSSII. TURTLES OF NORTH AMERICA. 



the ribs notch both the upper and the lower faces of the peripherals behind the seventh; in 

 0. erosus they notch only the upper borders. 



0. platylomus differs in having the anterior peripherals higher in proportion to their 

 length and in having the upper border of the first and second thicker. In O. platylomus the 

 rib-pits of the sixth and seventh peripherals are decidedly flattened; in 0. borealis they are 

 conical. 0. chelydrinus differs in having the free border of the hinder peripherals angulated. 



Osteopygis platylomus Cope. 

 Figs. 172-180. 



Osteopygis platylomus, Cope, Anier. Naturalist, III, 1869, p. 89; Cook's Geol. New Jersey, 1868 (1869), 

 p. 735; Ext. Batrach., Reptilia, Aves N. A., 1869, pp. 135, 137, and p. ii, figs. 38, 39; Vert. Cret. 

 Form. West, 1875, p. 258. Hay, Bibliog. and Cat. Foss. Vert. N. A., 1902, p. 441. 



The type of Cope's Osteopygis platylomus is a fragmentary specimen which belongs to the 

 Academy of Natural Science of Philadelphia. It was presented to that institution by Samuel 

 Ashhurst, having been discovered in the uppermost greensand bed of the Cretaceous, at Pem- 

 berton, Burlington County, New Jersey. It now consists of the anterior half of one neural, 



Figs. 172 and 173. Osteopygis platylomus. Portions of type. 

 172. Part of a neural. X. 173. Pygal, suprapygal, and tenth and eleventh peripherals. Xi. 



most of the suprapygal, a portion of the nuchal, wholes or parts ot all the peripherals of the 

 right side, except the fifth, wholes or parts of the first, third, sixth, eighth, ninth, tenth of 

 the left side, many fragments of costals and portions of the plastron. It appears that a few 

 parts have been lost since Cope described the specimen. 



Cope estimated the length of the carapace at 2 feet 2 inches. The writer regards the length 

 as having been close to 30 inches or about 750 mm. 



The fragment of neural (fig. 172) is crost by a sulcus and is therefore probably either 

 the thud or the fifth. It is deeply notcht in front for the preceding neural, and this notch gives 

 evidence that the neural was not the first one. The greatest width of the bone is 56 mm. 



The bone described by Cope as the "posterior vertebral" is really the suprapygal. Only a 

 portion of the left end of the nuchal remains. It is articulated to a portion of the first left 

 peripheral. The tree edge is obtuse and at the suture with the first peripheral the thickness is 

 17 mm. The bone extends backward from the free border a little more than 60 mm., to 

 articulate with the first costal. Here the thickness is only about 6 mm. The first marginal 

 scute occupies the outer end of the nuchal and the anterior end of the first peripheral. Along 

 the free border it is 58 mm. and it extends backward from the free border of the bone ^^ mm. 

 Cope states that the nuchal scute was confluent with the first vertebral; but the writer regards 



