TRIONYCHin.l. 



519 



the pits are broad and 



there are 5 of them in a 

 The thickness <>t the second neural is 8 mm.; that 



rounded, I he pits measure as in the Opal specimens. Usually 

 ine 20 mm. long, but sometimes as many as 6 and again as few as 4. 



f the sutural holder of the second costal, 

 near the distal end, 7 mm.; that thru 

 the middle of the width of the same 

 costal, 13 mm. 



Too little is known regarding Cope's 

 Trionyx radulus, originally found in 

 the Wasatch beds of New Mexico, to 

 identify the Bridget' specimens as the 

 same. In the Wasatch specimens the 

 smooth beveled band around the tree 

 border is much narrower than in the 

 Bridger carapaces, the ridges of the 

 sculpturing coming down in places close 

 to the edge. In the case of the costal of 

 Cope's fig. 1 5 the border near the pro- 

 jecting rib is cut off nearly square, with 

 a tendency of the upper layer to over- 

 hang. Nothing of this sort is seen in 

 any of the Bridger specimens. The 

 costals and the neurals of the Bridger 

 forms appear to be thicker than those 

 of the type of A. radula. The pits of 

 the latter, too, are smaller, there being 

 usually 6 in a 20 mm. line, instead of 5. 

 The ribs of A. radula do not stand out 

 so prominently on the under side of the 

 costals as they do in the specimens of 

 A. aqua. 



The specimen (plate 99) belonging 

 to the U. S. National Museum is taken 

 as the type of A . aqua. 



lies. 672 and 673. Amyda aqua. Carapace of type. X I 



672. Carapace. 



673. Vertebra 1 of carapace, seen from below, c.p. 2, r ./>. 8, rib-heads 



of second, and eighth costal plates; dot .v. 2, dor.v. S, second 

 and eighth dorsal vertebra'; ./., nuchal plate. 



Amyda uintaensis (Leidy). 

 Plate 100, rig. 1; text-figs, 674, 675. 



Trionyx uintaensis, Leidy, Proc. Acad. Nat. Sci. Phila. 1872, p. 267; Contrih. Ext. Vert. Fauna West. 



Terrs., 1873, pp. 178, 342, plate xxix, fig. 1. Cope, Vert. Tert. Form. Wist. 1884, p. 118; Contrih. 



Canad. PaIa?ont., II, 1891, p. 5. Hay, Bibliog. and Cat. Foss. Vert. N. A., 1902, p. 454. 

 Amyda uintaensis, Hay, Amer. Geologist, xxxv, 1905, p. 336. 



The present species was based on a nearly complete carapace which was procured by Dr. 

 Leidy during his stay at Fort Bridget, in the year 1872. It was found, it is stated, in the 

 Bridger deposits, at Dry Creek, about 10 miles from Fort Bridger. It is probable that Little 

 Dry Creek was meant. If so, the level is B. This specimen belongs to the Academy of Natural 



Sciences of Philadelphia, where the writer has been permitted 

 to study it. Originally little more than fragments were missing 

 tmm the right side, altho the left side was more damaged. 

 Now, however, it lacks the nuchal, which was originally present. 

 The specimen was kindly loaned to the writer with permission to 

 develop it further, and the result has been to find present most of 

 the plastron and some of the cervical vertebrae. 



The carapace (fig. 674) is nearly as broad as long, broadest 

 somewhat behind the middle of the length, very slightly concave 

 in outline near the middle of the front, sinuous along the sides, and truncated behind. As 

 stated bv Dr. Leidv, the carapace is about as convex as that of Platypeltis mutica. The length 



