TRIONYCHID^:. 



521 



The xiphiplastra are missing; but the notches in the right hypoplastron show that these 

 bones were articulated as in Platypeltis. 



Three cervical vertebrae were exposed in preparing the plastron, the sixth, seventh, and 

 eighth. All of these are turned backward, as if the head had been retracted within the shell. 

 The sixth has a length of 75 mm. The structure of these vertebrae resembles that of P. ferox. 



There is present also one ilium, but there appears to be nothing distinctive about it. 



This species is very distinct from Aspideretes guttatus, but it might be very difficult 

 to distinguish small fragments of the two. The last-named species has a much more elongated 

 shell and a preneural, characters which readily distinguish it from Amyda uintaensis. From 

 Amyda egregia, which has similar ornamentation, it is distinguish! by the different form of 

 the carapace and of the first neural; by the narrower neurals; and by the presence of 6, 

 instead of 7, of them. 



Amyda scutumantiquum Cope. 

 Plate 100, figs. 2-4; plate 101, fig. i; text-figs. 676, 677. 



Trionyx scutumantiquum, COPE, 6th Ann. Report U. S. Geol. Surv. Terrs., 1872 (1873), p. 617; Amer. 



Naturalist, xvi, 1882, p. 988, fig. 6; Vert. Tert. Form. West, 1884, pp. 118, 121, plate xvi, figs. 



i, la. HAY, Bibliog. and Cat. Foss. Vert. N. A., 1902, p. 454. 

 Amyda scutumantiquum, HAY, Amer. Geologist, xxxv, 1905, p. 336. 



The type of this species consists of a nearly complete carapace and a considerable part of 

 the plastron, which were found in the Bridger beds, on Cottonwood Creek, in Wyoming. This 

 specimen is now in the American Museum of Natural History and has the number 1035. 



''' 677. 



FIGS. 676 AND 677. Amyda scutumantiquum. X { 



676. Carapace. 



677. Plastron. Restored mostly from left half, 



partly from right. 



Professor Cope also referred to the same species, with some doubt, fragments which had been 

 collected from the Wasatch deposits near Black Butte, Wyoming, and from the same forma- 

 tion on Bear River. Where these Wasatch specimens now are the present writer does not 

 know. 



On the page facing plate xvi of the Vertebrata of the Tertiary Formations of the West, 

 Professor Cope states that his figures of this species are reduced to one-fourth the size of nature; 

 but this is an error, the figures being almost exactly one-third the natural size. 



This species attained a large size and possest a heavy shell. The length of the carapace 

 (plate 101, fig. i; text-fig. 676) of the type is 430 mm., measuring from the anterior portion 

 of the nuchal. The width is very close to 400 mm. There was probably a broad but very 



