288 FOSSIL TURTLES OF NORTH AMERICA. 
1. Shell smooth; no dorsal keel; crushing-surface of upper jaw 
with a feeble ridge; rib-heads well developt................ Chrysemys 
2. Surface of shell sculptured; rib-heads thread-like......... .... Detrochelys 
Shell smooth or wrinkled; crushing-surface of upper and lower 
jaws broad and flat; palatine bones joining vomer in front of 
ChOANZY cade Sars Boehner ne ee, ae ee ae Graptemy 
. Crushing-surface of upper jaw witli, a strong longitudinal ridge. 
4. “At least a trace of a dorsal keel; carapace often sculptured; 
crushing-surface of upper Be with a denticulated ridge highest 
in jane ae : ee ane Trachemys 
5. Crushing-surface of upper jaw very broad, with a denticulated 
longitudinal ridge; lower surface of lower j jaw flat <o.n2sn0020 Pseudemys 
b°. Plastron completely filling the opening of the carapace; furnisht with both 
lateral and transverse hinges. . yee ep eT en . Terrapene 
io) 
Genus GYREMYS nov. 
Shell deprest; as broad as long, or broader; with plastron and carapace sculptured as in 
the Trionychide; both furnisht with epidermal scutes, the vertebrals very broad. Carapace 
with a complete set of peripherals. Neurals mostly hexagonal, with the broader end forward. 
Plastron without fontanels, and joined to the carapace by means of anterior and posterior 
buttresses. Apparently no mesoplastra present. 
Type: Gyremys spectabilts. 
This genus differs from G/yptops, as represented by G. plrcatulus, in the form of the cara- 
pace, the width being greater than the length, and in the character of the ornamentation of the 
shell. The lack of mesoplastra, if confirmed, will be decisive in showing its non-relationship 
to Glyptops. Inthe latter genus, as well as in Pleurosternon, the suture between the hypoplastra 
and the xiphiplastra runs across the plastron in a straight line or is even deflected backward at 
the midline, apparently a primitive character; while in Gyremys the suture is deflected forward 
at the midline. 
Provisionally this genus is arranged with the Emydidz. No intergulars or inframarginals 
have been observed, bi they may nevertheless have been present. It is possible that the genus 
belongs among the Der matemydide. 
Gyremys spectabilis sp. nov. 
Plate 44, figs. 1, 2; text-figs. 357, 358. 
Under this name there is here described a remarkable turtle which was collected in 1876 
for Professor Cope, by Messrs. Sternberg and Isaac, in the Judith River deposits of Montana. 
Apparently the remains were never examined by Professor Cope, and the many fragments 
of which it was composed were put together after it came to the American Museum of Natural 
History. The specimen bears the Snel LIZ. 
The bones of this turtle were originally thin; and as a result of the conditions attending 
fossilization they have been much faetited, Consequently, it is difficult to determine fhe 
positions of some of the sutures and scutes, especially those of the carapace. 
As regards the parts remaining, the plastron is complete; the carapace lacks the nuchal 
bone, the right first peripheral, the left first costal, and several of the left peripherals. 
The shell was a remarkably broad and flat one. The total length of the carapace (plate 44, 
fig. 1; text-fig. 357) was about 440 mm.; the width, 500 mm. Hence, the shell was broader 
than long. As restored, the height of the carapace above the bottom of the plastron is only 
7omm. It was no doubt more elevated during life, but probably not much. 
The ornamentation of the shell consists, where distinctly displayed, of low, short, irregular 
ridges, separated by grooves of the same width, and occasionally anastomosing. ‘There are 
about five ridges in 10 mm. ‘The central portions of the carapace, however, are nearly smooth. 
In most parts of the shell the sculpture is so effaced that its character can hardly be determined, 
beyond the fact that it resembles that of the Trionychide. 
However, the relationships of this turtle are not with the Trionychidz, but with the 
Cryptodira; for the plastron is completely closed and the costals are surrounded by a complete 
