136 



FOSSIL TURTLES OF NORTH AMERICA. 



of the fifth costal at the distal end is 77 mm. At the costo-vertebral sulcus the seventh and 

 eighth costals (fig. 149) are each 39 mm. wide. The eighth is 47 mm. wide at the distal end. 

 On the inferior side of the eighth costal is seen the base of the small rib-head. Behind this is 

 the co-ossified end of the vestigial tenth rib. 



The surface of the bones of the carapace is almost everywhere more or less uneven. On 

 the nuchal and the anterior peripherals the areas occupied by the scutes are tumid, and the 

 sulci run in deep and broad valleys. The same remarks apply to the dorsal region of the 

 carapace, so far as represented. The sulci of the distal portions of the costals and of the hinder 



peripherals are deeply imprest. 

 The upper surfaces of the hinder 

 peripherals are more or less undu- 

 lating. 



The nuchal scute (fig. 147) is 

 smaller than that of either 0. 

 emarginatus or 0. gibbt; its width 

 anteriorly being 47 mm.; poste- 

 riorly, 80 mm.; its fore-and-aft 

 extent, 24 mm. The first marginal 

 is 62 mm. along the front; 30 mm. 

 where it joins the nuchal; 45mm. 

 where it joins the second marginal. 

 On the tenth peripheral the costo- 

 marginal sulcus runs 30 mm. 

 below the upper border of the 

 bone. At the midline behind, the 

 sulcus crosses on the hinder supra- 

 pygal. 



The anterior vertebral scute 

 had a width of about 200 mm. 

 On the fourth costal the costo- 

 vertebral sulcus crosses the bone 

 at a distance of about 44 mm. 



from the neural border. Esti- 

 mating the width of the neural at 

 45 mm. the width of the third ver- 

 tebral would be about 135 mm. 

 The fourth vertebral, at the ante- 

 rior border of the seventh costal, 

 appears to have been about 100 

 mm. wide. That of 0. gibbi was 



about 135 mm. wide. The fifth vertebral had a width posteriorly of 190 mm. Its length was 



close to 155 mm. 



On account of the common feature of sutural union of all the peripherals with the costals, 



this species needs comparison only with O. emarginatus and O. gibbi, and such comparisons 



have already been made. 



Osteopygis chelydrinus Cope. 



C 



FIGS. 148-151. Osteopygis robustus. Costals, peripherals, 

 and pygal of type. 



148. Section at proximal end of first peripheral. X$. 



149. Right seventh and eighth costals, hinder peripherals, and pygal. xj. 



150. Section of anterior end of tenth peripheral. X. 



151. Section along middle of pygal. Xj. 



Plate 23, figs. 4-7; plate z8, figs. 1-4; text-figs. 152-154. 



Osteopygis chelydrinus, COPE, Proc. Acad. Nat. Sci. Phila. 1868, p. 147 (nom. nud.); Geol. New Jersey, 

 Cook, 1869, Append., p. 735 (nom. nud.); Amer. Naturalist, in, 1869, p. 89; Ext. Batrach.. 

 Reptilia, Aves N. A., 1869, pp. 135, 138, plate vii, fig. 8. HAY, Bibliog. and Cat. Foss. Vert. 

 N. A., 1902, p. 441. 



Catapleura chelydnna, COPE, Vert. Cret. Form. West, 1875, P- 2 59- 



In his Synopsis of the Extinct Batrachia, Reptilia, and Aves of North America, Professor 

 Cope stated that this species was represented by "only 10 marginal plates more or less perfect 

 and some costals"; also that the species was referred to the genus Osteopygis because the 



