1 82 



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 ol 

 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 Toxochelys. 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 



rlG. 234. Port hoc helys aticeps. Lara- r -r 11 1 1 j- 1 u L J' .. J 



j * . , y t, j of Toxochelys; but the radial process has been directed 



pace of type. X. 1 ,. Restored por- J . r . , , , , , r 



j- ik a ., a v o more strongly toward the ulnar side. 1 he total length ol 



tions indicated by dotted lines. , 6 y t, 



the bone was 140 mm. 1 he position and extent ol the 

 epicondylar groove and of the condyles for the radius and ulna seem to have been the same as 

 in Toxochelys. Two cervical vertebrae, a small portion of the scapula, and a claw are mentioned 

 by Williston as furnishing no important differences when compared with those of Toxochelys. 

 In general appearance this turtle differs greatly from Toxochelys. The head is ot 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, xxi, 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 ot 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. 



