PLEUROSTERNID&. 49 
goid processes are very large. The anterior region of the roof of the mouth is damaged, 
so that little is to be learned from it. 
The lower jaw is closely prest against the remainder of the skull. From its tip to the 
hinder end is 54 mm. The two rami are co-ossified. The symphysis is 10 mm. long. All the 
bones are smooth. 
Here it may be permitted to make some remarks on Bautr’s description of the 
skull of this species. The sculpture of the bones is not exactly like that of the shell, 
it being finer and more pustular. Baur, in opposition to Marsh, states that the 
exoccipitals take part in the formation of the condyles. It seems probable that 
Baur came to this conclusion from the presence of the pit, making the assumption 
that this is found only where the basioccipital meets the exoccipital. In the skull 
of a Bridger Baéna the basioccipital takes no part in the condyle, and yet there is a 
very distinct pit. The skull of G/yptops in the American Museum does not enable 
us to decide the question. 
Portions of 7 of the cervicals are preserved in the American Museum specimen, the first 
not being present. As a whole, the neck seems to have been short and slender. Its total 
length did not exceed 120 mm., the carapace being 300 mm. The articular end of the second 
cervical has a diameter of only 4 mm., while that of Trachemys elegans, with a carapace 230 mm. 
long, has a diameter of 5 mm. All the cervicals present a deep, comprest, and sharp keel along 
the lower side, thickening behind. All, excepting probably the first, possest transverse pro- 
cesses, each about 4 mm. long. All have the anterior and posterior articular surfaces more or 
less concave. The hinder end of the eighth is concave, without the convex portion men- 
tioned by Dr. Baur. The anterior end also is concave. The postzygapophyses are close 
together, but have not coalesct. The hinder end of the seventh is nearly flat, and we may 
suppose that it has entered on the first stages in forming a convex articulation. Barring the 
articular surfaces, these cervicals resemble closely those of Baéna. 
The first dorsal vertebra has a very distinct keel along its lower side and the anterior end 
of the centrum is concave. The first rib is long, about 57 mm., and has apparently lost a 
portion of its extremity. It has a diameter of about 5 mm. and is applied closely to the rib of 
the first costal plate. The rib-heads are much like those of Baéna. The one belonging to the 
first costal plate is the broadest, about 12 mm. in diameter. Most of the others are smaller, 
about 8 mm. wide. The last two are considerably smaller. The tenth rib is short and thick, 
its length being 15 mm., its diameter 4 mm. Its outer end is somewhat enlarged, to support 
the ilium, and it is applied against the lower surface of the eighth costal. The first sacral rib is 
the larger, about 20 mm. long, and expanded at its outer end to a width of ro mm. The 
second sacral rib is much slenderer. Both of them resemble corresponding parts of Chelydra 
and Baéna. 
The carapace (plate 6; text-fig. 17) is 300 mm. long in the midline, and 272 mm. wide. It 
is much deprest, but this is due to some extent to distortion during burial, for some of the 
costals and peripherals are spread apart. Anteriorly the border is slightly excavated in the 
midline. Posteriorly the carapace is truncated and broadly and shallowly excavated. Marsh’s 
figure represents his specimen as more rounded behind. The peripherals extended outward 
nearly horizontally. Their borders are subacute near the midline in front and behind, but 
they thicken and become more obtuse toward and over the 
{hig eee bridges. The whole surface of the carapace and of the plastron 
Neural. Length. Width. | . ; Pics : fi 
| is finely sculptured with tubercles and winding ridges, there 
i eee 7 | | being about 12 ridges in a line 10 mm. long. 
I 33 | The nuchal bone is quadrilateral, with the broadest side 
g | a | joining the first costals and the first neural. This side is 80 
s 3 co a . ° 
4 260 | (23 mm. long. The free border is 42 mm. long. The accompanying 
5 27h we Nh 23 | table presents the dimensions of the neurals. 
I 1 . . . . . 
; 3 Fs There is in this specimen a single suprapygal. Baur states 
8 18 2K | that in the Yale specimens there are two of these bones, but 
| 
| 
| 
Marsh figures only one. A sketch in the writer’s possession, 
