388 



FOSSIL TURTLES OF NORTH AMERICA. 



plastra on each side of this are rounded. The bone of the plastron is relatively thick. In the 

 case of a specimen whose plastron is 210 mm. long the thickness of the hyoplastron is 16 mm.; 

 that of the hypoplastron half-way between the median line and the inguinal notch is 14 mm. 

 Proceeding backward from the inguinal notch near the free border there is a low wall from the 

 summit of which the bone slopes downward and outward. Farther backward the height of 

 the wall diminishes rapidly and the slope is less steep, so that on the apices ot the xiphiplastra 

 the sloping face looks nearly upward. From the summit ot the wall the surface slopes very 

 slowly toward the midline. 



The gular scutes overlap slightly the entoplastron. The humero-pectoral sulcus crosses 

 the midline just behind the entoplastron. The pectoral scutes are rather narrow at the mid- 



486. 



Figs. 486 and 487. Stylemys nebrascensis. X 3. 



486. Carapace. 



487. Plastron. 



line. The abdominals are the widest of the plastral scutes. At the midline the temorals are 

 about as wide as the pectorals. The anals occupy somewhat more of the midline than do the 

 femorals. Small axillary and inguinal scutes are present. 



Figs. 1 and 2 of plate 62 furnish illustrations of the shell of a specimen of the species, No. 

 1453 of the American Museum of Natural History. The figures are half the natural size. 

 I ext-figs. 48A and 487 are derived from the same specimen. 



It is remarkable that, notwithstanding the great number of individuals of this species which 

 have been found, few skulls have hitherto been discovered. Leidy, writing manv years ago, 

 stated that he had seen hundreds of shells but no skull. The one here described as probably 

 belonging to this species belongs to Princeton University. 



This specimen (plate 59, figs. 2, 3) was collected by Mr. J. W. Gidley, now of the U. S. 

 National Museum, in the year 1896. It was found in the Oreodon beds of the Hat Creek 

 Basin, near Prairie Dog Creek, Nebraska. It was not accompanied by any other parts; but 

 in the White River deposits of that region Stylemys nebrascensis is abundant; and no other 

 related species, except one specimen of Testudo brontops, of the Titanotherium beds and T. 

 thomsom of the lower Oreodon beds has been found in the White River Oligocene; so that the 

 probability is very great that the skull belongs to this species. This probability is confirmed 

 by the skull next to be described. 



Unfortunately, the Princeton skull is not complete. The hinder segment is missing, as 

 well as the quadrates. There is likewise no lower jaw present, and there are some minor 

 deficiencies, 



