540 FOSSIL TURTLES OF NORTH AMERICA. 
have been quite vestigial. “The costals of the first pair are, at their proximal ends, much 
wider fore and aft than those behind them, being about 53 mm. wide, and they increase in width 
toward their distal ends. The third and fourth costals are narrow at their proximal ends, 
ote” en being respectively 36 mm. and 33 mm. wide, and they 
ar ee expand little toward the distal ends. The fifth and sixth 
= —— ~ are likewise narrow proximally, but they expand rapidly 
, 4 toward the margins of the carapace. The seventh cos- 
m \ tals extend on each side about 66 mm. from the midline. 
{ 3 \ The free ends of the costal ribs extend little, if any, 
. . ; beyond the margins of the carapace, thus affording evi- 
cme dence that the individual was an aged one. 
= 4p as J The carapace is thick and solid. Near the proximal 
} | ~~~) ends the costals are 6.5 mm. thick and this thickness 
i ou increases toward the margins of the carapace, where it 
ae le cE ees amounts to 8 mm. in front and behind, and to 12 mm. 
| ' + and even 15 mm. at the sides. The borders of the cara- 
\ ' pace are not beveled off as in many species. Anteriorly 
_ ~ and posteriorly the edge is rounded; at the sides the 
a / upper layer of bone ov erhangs the lower, and a groove 
: / runs along between them. 
There was probably no preneural. The first neural 
= ey, is missing, but the proximal border of the left first costal 
‘ 7 Se: 
H ” i indicates that the neural was long and narrow, with the 
te narrower end forward. Only a fragment of the second 
neural remains. The third neural had a maximum width 
Fic. 703.—Flatypeltis extensa. Cara- Of about 23 mm.; the fourth a width of 20 mm.; the fifth 
pace of type. X }. a width of 17 mm. The more posterior neurals have not 
been preserved. 
The nuchal bone is relatively small. Its lateral extent is 158 mm.; its fore-and-aft measure- 
ment, 29 mm. The outline of the anterior border is nearly straight, and the immediate edge 
is rounded and about 7 mm. thick. 
The sculpture of P. extensa resembles closely that of P. heteroglypta, consisting of large 
pits, about two 1n a line 10 mm. long, on the neurals and the proximal ends of the eoatale. and 
of smaller cells, three 1n 10 mm., on the distal ends of the costals. The large pits have broad, 
low, and rounded walls surrounding them, while the walls of the smaller pits are more sharply 
defined. On the outer ends of the ‘ostals the pits show some tendency to arrange themselves 
in rows parallel with the margins of the carapace, 
This species differs from P. heteroglypta in its greater breadth as compared with the length, 
and in the thickened and grooved lateral borders of the carapace. 
The left hyoplastron and hypoplastron are complete, except the tips of the outer processes. 
The two bones are thoroly co-ossified. The sculptured layer, the callosities, extends to 
the midline. The length of the hyohypoplastral suture is 176 mm. The width of the bridge 
is 62 mm. Here the thickness of the hypoplastron is 11 mm. The hyoplastron is somewhat 
thinner. Near the inner end of the anterior border of the latter bone there is a deep notch for 
the entoplastron. At the hinder outer angle of the hypoplastron is a notch for a process of the 
xiphiplastron. The humerus differs only j in details from that of P. spinifera. Its total length 
is 87 mm. 
Platypeltis leucopotamica (Cope). 
Plate 113, figs. 1-3; text-fig. 704. 
Trionyx leucopotamicus, Cope, Contrib. Canad. Paleont., 11 (4 to), 1891, p. 5, plate i, figs. 8, ¢.—Amr, 
Science (1), Xvi, 1891, p. 53.—Hay, Bibliog. and Cat. Foss. Vert. N. A., 1902, p. 454. 
Trionyx punctiger, Cope, Contrib. Canad. Paleont., m1 (4 to), 1891, p. 5.—Hay. loc. cit. » P- 454. 
The type of this species is a fragment of a costal plate 33 mm. long and 25 mm. wide, 
which was found in the White River deposits of the Cypress Hills, District of Alberta, British 
America. Professor Cope’s description was reinforced by some fragments of what he regarded 
as the same species, which he had obtained in the White Buttes of North Dakota. One of 
