120 



FOSSIL TURTLES OE NORTH AMERICA. 



is 420 mm. and the maximum width 394 mm. There are 8 pairs of costal plates and 6 neurals. 

 The nuchal extended from side to side 240 mm., and from front to hack 56 mm. There is 

 no fontanel behind the nuchal. The neurals are, in general, rather narrow. The anterior two 

 are coffin-shaped, with the narrow end directed forward; the next two are nearly quadri- 

 lateral; the fifth coffin-shaped, with the broad end forward, while the sixth is cordate and 

 much reduced in size. The table presents the length and the maximum breadth ot the neurals. 



Of the costal plates, the first is broader than any of the others at the proximal end. The 

 second and the sixth are wider than any others at the distal end. The eighth is very short in all 

 directions. On account of the absence of the seventh and eighth neurals and the reduction ot 

 the sixth, the three hindermost pairs of costals meet in the midline. The rib of the fourth 

 right costal is present and projects beyond the border of the costal about 30 mm., being 28 mm. 

 wide at the base. Similar ribs have extended beyond the other costal plates, except the seventh 

 and the eighth. The costal plates are about 5 mm. thick. 



The sculpture resembles that of Aspideretes guttatus but is coarser. There are from 4 to 

 7 pits in 20 mm., usually five, the pits being quite irregular in size and grouping. From their 

 summits the walls between the pits slope gradually to the bottoms of the latter. 



674. 



Figs. 674 and 675. Amyda uintaensis. Carapace and plastron of type. Xs. 



f>74- Carapace. 



675. Plastron, cer.v. 6, cer.v. 8, sixth and eighth cervical vertebra; enl, entoplastron; /.</>/, r.epi, left and right 

 epiplastron; l.hyo, r.kyo, left and right hyoplastron; r.hvpo, right hypoplastron. 



The hyoplastron and the hypoplastron of the right side are complete, excepting that the 

 extremities of the external processes are broken away (plate ioo, fig. I; text-fig. 675). On 

 the lelt side there remains only a fragment of the hyoplastron. The right and the left branches 

 of the entoplastron are present, but the median and anterior part is missing. On the right side 

 is seen the anterior portion of the epiplastron, while the posterior part of the left epiplastron 

 lies close to the corresponding part of the entoplastron. 



Judging from the fragments of these parts of the plastron that remain, the entoplastron 

 and the epiplastra were not especially different from those of Platypeltis ferox. 



The hyoplastron is not co-ossified with the hypoplastron. The suture is directed inward 

 and forward, so that the anterior bone is narrower than the one behind it. The greater portion 

 of these bones is covered with a large callosity. This is ornamented on the external ends of 

 the bones with pits which resemble those of the carapace, but are not so large, there being 

 about five in a line 10 mm. long. The inner ends of the bones are smooth, hut display a cloth- 

 like texture, produced by interwoven fibers of bone. 



