140 



FOSSIL TURTLES OF NORTH AMERICA. 



thirds is rough, indicating sutural union with the second costal. Probably the sixth peripheral 

 was free from union with a costal; also the seventh. The hinder portion of the border of 

 the eighth peripheral is rough, as if it had formed a suture with the contiguous costal. The 

 upper borders of the succeeding two peripherals are broken away, so that we can not determine 

 their mode of connection with the costals. The eleventh peripheral articulated suturallv with 

 the suprapvgals. 



The first costal bone (fig. 155) has an extreme width of 104 mm. The outer end of its 

 rib was inserted in the third peripheral. In front, where it articulated with the nuchal, it is 

 10 mm. thick and the suture is beveled in a manner to show that the nuchal slightly overlapt 

 the costal. The hinder border is 9 mm. thick. Another costal has a width of 72 mm. and a 

 thickness of 10 mm. The rib is not conspicuous on the under side. 



The two neural bones are probably the third and fourth (fig. 162). Measured along the 

 midline the bone anterior is 84 mm. long, while the width is 42 mm. The anterior end is 

 narrowly notcht tor the reception of the preceding neural. There is no definite angle between 

 the antero-lateral and the postero-lateral sides. The other neural is 61 mm. long and 40 mm. 

 wide. 



The sulci which mark the boundaries of the horny scutes are extremely distinct, becoming 

 sometimes deep and broad. The outer end of the first marginal is 46 mm. wide. The second 



Figs. 156-162. Osteopygis erosus. Portions of shell of type. No. 1130 A. M. N. H. 



156. Section of first peripheral. <-. 



157. Hinder end of second peripheral. 



pit for process of hyoplastron. 



158. Section of fourth peripheral. Xg. 



159. Section at anterior end of sixth peripheral. X5. 



<. Shows 160. Section at middle of length of eighth peripheral. <. 



161. Hinder end of tenth peripheral. . 



162. Two neurals. X\. 



extends from the free border 55 mm.; the third, 41 mm. Behind this, the costo-marginal 

 sulci run along on the upper borders of the peripherals. From the upper borders of the 

 eleventh peripheral the sulcus crost on the last suprapygal, not coming into contact with the 

 pygal. The first vertebral scute appears to have been as in O. emarginatus. Its width can 

 not be determined. 



All the bones of the carapace are more or less rough and uneven, but that which especially 

 distinguishes them is the presence of numerous pits. These vary in size, depth, and distri- 

 bution. The average diameter is about 5 mm. These pits are relatively few on the anterior 

 portion of the carapace. They are numerous on the costals, and present commonly on the 

 peripherals (plate 26, fig. 2). 



The fragments of the plastron furnish no useful information. 



Accompanying the bones are a scapula and an ilium. The upper end of the scapula 

 and the distal end of the procoracoid process are broken off. The remainder of the bone 

 resembles the same bone in Caretta caretta. The ilium is broader and flatter above than in the 

 genus just named. 



