182 FOSSIL TURTLES OF NORTH AMERICA. 
the width being 785 mm., the length only 730 mm. The border appears to have been slightly 
excavated in front, elsewhere somewhat repand. The costal plates are so extensively ossified 
that there now remain only insignificant fontanels at their outer ends. The greater portion of 
the nuchal bone is missing. The peripherals are eleven in number on each side. They are 
rather narrow in front but their width increases posteriorly, and they become quite thick. 
The sixth from the front is equal in width to one-eighth of the width of the carapace; the eighth 
is a little more than one-sixth of the width of the carapace. 
Of the neurals the fifth and sixth are wholly wanting, while the fourth and seventh are 
represented each by only a small portion. Those present are narrow, about 30 mm.wide. The 
= — second, third, and fourth have their anterior outer angles 
cut off by contact with the costals in advance. ‘The 
neurals are smooth, and without trace of the tubercles 
which are so conspicuous in J oxochelys. There are two 
suprapygals, each forming a symmetrical trapezoid, and 
these are placed base to base. 
Dermal scutes were present, and are indicated by very 
distinctly markt sulci. The vertebrals are narrow, the 
third and fourth being about one-seventh as wide as the 
shell. The first is slightly wider; the fifth has a width 
equal to one-fourth the width of the shell. The mar- 
ginal scutes lie almost wholly on the peripheral bones. 
The plastron (plate 31, fig. 3) resembles greatly that 
of Toxochelys. There were small central and lateral 
fontanels. Probably the right and left halves of the 
plastron approacht each other more closely than is 
shown in the figure. The thickness of the hyoplastron 
and hypoplastron where they join is from 10 to 12 mm. 
They are thin and serrated along the median border. 
The right humerus accompanies the remains, but the 
ulnar process is broken away. The bone is flattened, 
mostly as a result of compression during burial. It 
appears to have resembled closely the corresponding bone 
of Toxochelys; but the radial process has been directed 
Fic. 234.—Porthochelys laticeps. Cara- 
pace of type. 3. Restored por- 
fone aicared by dotted lines: more strongly toward the ulnar side. The total length of 
the bone was 140 mm. The position and extent of the 
epicondylar groove and of the condyles for the radius and ulna seem to have been the same as 
in Toxochelys. Two cervical vertebra,a small portion of the scapula,and a claw are mentioned 
by W illiston as furnishing no important differences when compared with those of Toxochelys. 
In general appearance this turtle differs greatly from Toxochelys. The head is of heavier 
construction and of blunter form; there are nasals; the carapace is circular, instead of 
elongated and pointed behind; it is more extensively ossified; and there is no carina along the 
middle of the back. Otherwise Porthochelys agrees with Toxochelys. As already remarkt, 
the presence of nasals is regarded as being of no more than generic value. 
Porthochelys browni Hay. 
Figs. 235-237- 
Porthochelys browni, Hay, Bull. Amer. Mus. Nat. Hist. xx1, 1905, p. 183, figs. 15, 16. 
The type of this species was collected during the summer of 1903, by Mr. Barnum Brown 
of the American Museum of Natural History, in deposits shown by their invertebrate fossils 
to belong to the Pierre formation. The locality is 20 miles southeast of Edgemont, South 
Dakota. The catalog number of the specimen is 6080. 
The specimen presents the skull and the lower jaw nearly complete, some pelvic bones, 
one humerus, one scapula, a femur, and some other limb bones. Unfortunately most of the 
bones are crusht nearly flat and were covered with a layer of gypsum. Altho the skull is consid- 
erably crusht, the most essential elements of its construction may be determined. 
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