400 FOSSIL TURTLES OF NORTH AMERICA. 
bridge peripherals extend upward about 140 mm. above the slight carina 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 100 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 1s 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 he in deep valleys. The supracaudal scute is 175 mm. wide at 
its lower end. Its upper end overlaps the gee suprapyg veal bone. 
The plastron (plate 65, fig. 2; text-fhg. 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 ae bilobed anterior border. The length of the lip beyond the points where the gulo- 
humeral sulci cross the free borders of the epiplastra i is 56 mm.; the width at the base is 135 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 midhne: the femorals, 100 mm; 
and the anals, about 60 mm. 
A large specimen of Testudo was collected in the Titanotherium 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 vertebra, 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. 
