54 



FOSSIL TURTLES OF NORTH AMERICA. 



A specimen of a large trionychid collected in 1903, in the western part of Grizzly Buttes, 

 is referred to this species. Its catalog number in the American Museum of Natural History is 

 5917. It consists of the outer ends of the nuchal, the greater portion of the right first costal, 

 the outer ends of the left first and second costals, various portions of other costals, 1 neural, and 

 fragments of other parts of the skeleton. The individual was a large one. The first costal 

 near its proximal end was about 75 mm. wide fore and aft; the second costal has a width 

 equally great. The sculpture appears to be identical with that of No. 6005, consisting of large 

 flat-bottomed pits, surrounded by walls with rounded summits. As in No. 6005, there is a 

 band near the free margins of the carapace which has no pits, but which presents a fine net- 

 work of bony fibers, resembling a textile fabric. On the rear of the carapace of No. 6005 this 

 band is narrow. In the case of No. 5917 the band is considerably broader, 25 mm. or more. 



Figs. 663 and 664. Aspideretes guttatus. 



663a. Carapace. Xj. 



664a. Pelvis, seen from left side. X^ 



6636. Plastron. Xj. 



6646. Pelvis, seen from below. Xj. 



The width of the outer end of the nuchal bone exceeded 65 mm. The length of the bone from 

 side to side was about 230 mm. Apparently only a relatively narrow strip on the posterior 

 border of the nuchal was occupied by a pitted surface. In front of this there was an area 

 about 25 mm. wide with the textile-like appearance noted above. The ends of this element 

 present ordinary bony tissue. The outer extremities of the nuchal overlapt the free ends of 

 the ribs of the first costals. 



The sutural borders of the costals present a band devoid of pits and is finely striated at 

 right angles to the sutures. 



Future discoveries must decide whether or not this identification of No. 5917 is correct. 



Still another specimen, No. 5993, collected in 1903, in the eastern part of the Grizzly 

 Buttes, must for the present be referred to A . guttatus. The carapace is nearly complete, but, 



