400 FOSSIL TURTLES OF NORTH AMERICA. 



bridge peripherals extend upward about 140 mm. above the slight canna which joins the border 

 of the third peripheral with that of the seventh. From the seventh peripheral the height of 

 these bones diminishes to the pygal. The latter has a height of 82 mm.; a width of 125 mm. at 

 the upper border, and of IOO mm. at the free border. 



The nuchal scute is 56 mm. long and only 7 mm. wide. The first vertebral has a width of 

 230 mm. in front and a length of 165 mm. The transverse extent of the vertebral scutes is con- 

 siderably less than that of the costals. The width of the second is 190 mm.; that of the third 

 probably about the same, but its lateral boundaries are mostly hidden; that of the fourth is 

 150 mm.; that of the fifth, at the posterior end, is 180 mm. The second costal scute has a trans- 

 verse extent of 230 mm. 



The sulci between the anterior marginal scutes lie in grooves; and, as they approach the 

 free border, they curve toward the midline. Those of the bridge region are directed forward at 

 their lower ends. The lower ends of these sulci and the longitudinal ones between the marginal 

 and the plastral scutes also lie in deep valleys. The supracaudal scute is 175 mm. wide at 

 its lower end. Its upper end overlaps the posterior suprapygal bone. 



The plastron (plate 65, fig. 2; text-fig. 505) is quite concave, a condition which indicates 

 that the animal was a male. The length of the anterior lobe is 222 mm.; its width is 380 mm. 

 The anterior lip extends beyond the border of the carapace about 60 mm. It projects boldly 

 from the general contour of the anterior lobe and its lateral borders converge somewhat as they 

 approach the bilobed anterior border. The length of the lip beyond the points where the gulo- 

 humeral sulci cross the free borders of the epiplastra is 56 mm.; the width at the base is 1 35 mm. 

 A broad and deep groove occupies the median line of the lip and ends in the notch in the front 

 of the lip. The greatest thickness of the lip is 50 mm. The superior surface is somewhat 

 convex from side to side. In all probability there is an excavation in the hinder portion of the 

 lip above, but the matrix has not been removed. 



The entoplastron has a width of 175 mm. and a length of 120 mm. The bridge is 300 mm. 

 wide. The hinder lobe has a length of about 175 mm. and a width, at the base, of 370 mm., or 

 slightly less. The notch in the rear is about 40 mm. deep and about 100 mm. wide. The xiphi- 

 plastra are each 165 mm. long. Just behind the inguinal notch the border of the posterior lobe 

 is 50 mm. thick and forms a nearly perpendicular face. Further backward the steepness of 

 the slope and its height are rapidly reduced. 



The sulci bounding the dermal scutes are deeply imprest. Those bounding the gular 

 scutes lie at the bottom of deep valleys, which proceed forward from the entoplastron, one to 

 each side of the base of the lip and one to the front on the midline. The gulars encroach some- 

 what on the front of the entoplastron. The humero-pectoral sulcus starts on each side at the 

 axillary notch, runs inward and backward, then inward and forward. Near the midline it is 

 somewhat irregular, bending in its course slightly backward. On the left side it traverses 

 the border of the entoplastron. The width of the pectoral along the midline is between 

 50 mm. and 60 mm. The abdominals occupy 240 mm. of the midline; the femorals, 100 mm; 

 and the anals, about 60 mm. 



A large specimen of Testudo was collected in the Titanothenum beds of South Dakota by 

 the party from the American Museum in 1904. It appears to belong to this species. 



This species is especially interesting because of its being the oldest known North American 

 species of the genus. T . ammon, described from the Upper Eocene of Egypt, appears to be 

 still older. 



Testudo thomsoni sp. nov. 

 Plate 66, figs. 1-5. 



The only remains of this species at present known were obtained in 1904, by Mr. Albert 

 Thompson, of the American Museum of Natural History, at Corral Draw, in Ziebach County, 

 South Dakota. They were found in a block of limestone which had come from the Lower 

 Oreodon beds. The parts secured are the skull, the greater portion of the anterior lobe of the 

 plastron, some cervical vertebrae, and parts of the left foreleg. These bear the catalog number 

 3940. Other portions of the skeleton were in the block; but they were not secured, because 

 they were supposed to belong to the very common species, Stylemys nebrascensis. 



