148 FOSSIL TURTLES OF NORTH AMERICA. 
laterally. The distal end of a costal bone is 70 mm. wide. The surface of the bones is usually 
moderately smooth, but markt by irregular, rather straight, vascular grooves. The sulci are 
usually quite distinct. 
The nuchal scute is present, as stated. Its lateral extent is conjectural; the fore-and-aft 
width is about 30 mm. The widths of the vertebral scutes can not be exactly determined; 
but they all appear to correspond closely to those of O. gibbi Wieland. The first evidently 
Fics. 175-180.—Osteopygis platylomus. Peripherals and sections. 
Type. X#. 
175. Sixth, seventh, and eighth right peripherals. 
176. First, second, third, and fourth right peripherals. 
177. Sections of first and second left peripherals. a, distal end of second; }, 
proximal end of second; c, near proximal end of first. 
178. Hinder end of eighth: peripheral. 
179. Front end of eighth peripheral. 
180. Section along right articular border of the pygal. 
extended laterally to about the middle of the first peripheral. The 
eleventh reacht laterally the hinder border of the pit for the last rib. 
The costo-marginal sulci run along on the upper borders of the first and second peripherals, 
then disappear, to reappear on the upper borders of the eighth to the eleventh. From the 
third to the eighth peripherals the sulci occupied doubtless the space between the costals and 
the peripherals. 
At present there remain of the plastron only a part of the left hyoplastron, most of the left 
hypoplastron, and most of the right xiphiplastron. The plastron seems not to have differed 
in any important way from that of O. borealts. Evidently there was a fontanel between the 
hyoplastra in front and the hypoplastra behind. At the narrowest part of the bridge the hypo- 
plastron is 58 mm. wide. The thickness at the inguinal notch is 16 mm. No sulci are to be 
seen on these bones, except a faint one near the base of the xiphiplastron. To the present 
writer it seems evident that the bones on the right of Cope’s figure of the plastron of this species 
