506 FOSSIL TURTLES OF NORTH AMERICA. 
in the American Museum of Natural History is 5930. The convexity and the outline of the 
carapace are very similar to those of the type. The front margin is somewhat more excavated 
than in the type, and the lateral borders are more sinuated. This is caused by the extension 
of the sculptured layer out on the distal ends of the ribs. 
The length of the specimen is 450 mm.; the greatest width, 380 mm. The preneural is 
relatively broader anteriorly than in the type, and the sixth neural is not developt. In the 
latter respect we may find variations in our living species of Trionychide. 
With this specimen from Wyoming comes a considerable portion of the plastron. This 
includes the median half of the left and a fragment of the right hyoplastron, and a considerable 
part of the right hypoplastron. These bones are thick and heavy, the thickness of the bones 
along the suture joining them on the narrowest part of the bridge being 16 mm. From this 
point the thickness is reduced each way to about 10 mm. at the median: and outer borders of 
the bones. At the narrowest part of the bridge the width of the hyoplastron is 50 mm.; of the 
hypoplastron, 42 mm. The xiphiplastron ihas joined the hypoplastron by the hel two 
digitations. The lower surfaces of the hyoplastra and the hypoplastra are occupied by a 
Fics. 665 AnD 666.—Asprderetes ellipticus. 
665. Carapace of type. X14. 666. Plastron. X}. 
nearly obsolete sculpture of pits and ridges. This is most distinct on the outer ends of the 
bones, where we find 3 pits in a line of 10 mm. This sculpture and the bone supporting it 
have approacht nearly to the midline, an indication that the individual was an old one. 
The hyoplastra and hypoplastra resembled closely those of Platypeltis ferox, of Florida. 
Text-fig. 666 represents what is known of the plastron of this species. The figure is con- 
structed partly from the specimen just described, partly from the following one. 
A still larger example of this species was collected during the summer of 1903 near the 
mouth of Cottonwood Creek, Wyoming. Its catalog number in the American Museum of 
Natural History is 5979. The bones of the iedan line and of the left side are complete, 
except that the third neural is wanting and portions of the fifth, sixth, and seventh costals. - 
Some parts of the right side are present. The right hyoplastron is quite complete. 
The length of this specimen is 510 mm.; the width was close to 445 mm. It displays a 
greater convexity of the carapace than is seen in the other specimens. The nuchal and the 
preneural resemble closely those of the type. The sixth neural is present, but small. Altho 
the individual was so large and evidently aged, the free ends of the ribs project beyond the 
margin of the carapace a distance of about 40 mm. The hyoplastron is identical with that of 
