TRIONYCHIDiE. 517 



sutural edge on one side. At the junction of the sutural border with the free border, the thick- 

 ness is 10 mm. On the sutural border, at the end of the fragment toward the midline, the 

 thickness is reduced to 8 mm.; that is, this costal is thicker at the outer end than nearer the 

 midline. This and other fragments show that the free ede, on each side ot the rib extension, 

 u .is cut off at nearly right angles with the sculptured surface. The sculpture came down close 

 to the distal ends of the costal plates. In some cases, but not all, there is a tendency for the 

 pits to arrange themselves, at the ends of the costals, somewhat parallel with the tree border 

 ot the bone. 



Fig. 5 (fig. q of Cope) is a portion of the costal plate of a small individual. The width is 

 21 mm.; the thickness, only 4 mm. Fig. 6 (fig. 8 of Cope) represents a fragment from prob- 

 ably the proximal end of a costal plate. Here the ornamentation consists of tubercles and 

 short, winding, and occasionally anastomosing, ridges, the pattern being somewhat coarser 

 than that ot the plastron, there being two furrows or pits in about 5 mm. This is true of most 

 of the ornamentation of the carapace. 



Amyda radula (Cope). 

 Plate 86, figs. 11, 12. 



Trionyx radulus, Cope, Systematic Cat. Vert. Eocene New Mexico, 1875, p. 35; Report on Geol. 

 N. W. N. Mex., in Appendix Ann. Rep. Chief of Engineers, 1875, p. 1015 (of separata, p. 95); 

 Wheeler's Surv. W. 100th Merid., IV, 1877, p. 45, plate xxvi, figs. 11-16. Hay, Bibliog. and Cat. 

 Foss. Vert. N. A., 1902, p. 454. 



In his original description Professor Cope characterized with great brevity this species of 

 Amyda. In his final report on his explorations in New Mexico, publisht in the fourth volume 

 of the Wheeler Survey, he gave some additional data and figures of some of the fragments on 

 which he had based the species. Even here, however, the description is limited to 10 lines of 

 print. The type specimens are now in the U. S. National Museum, at Washington, No. 2581. 

 They were collected 111 \\ asatch deposits along the Gallinas River, New Mexico. 



The figures given by Professor Cope make the summits of the ridges surrounding the pits 

 appear too broad. They are really narrow. From their summits the walls slope rapidly to the 

 bottoms of the pits, but not so abruptly as the figures indicate. 



Cope's fig. 1 1 represents the distal end of a costal. It has a thickness of 6 mm. In the 

 original of fig. 13 the free border, at the side of the extension of the rib, is cut off nearly square, 

 with a tendency of the upper layer to overhang. It will be observed that the sculpture of this 

 and of the costal of his fig. 14 I plate 86, fig. 1 1) comes down close to the free border of the bones. 

 Cope's fig. 15 (plate 86, fig. 12) represents the middle of a costal. The sutural border is 4 mm. 

 thick. There are 6 pits in a line 20 mm. long. His fig. 16 is that of a neural which has a thick- 

 ness of 6 mm.; and there are 5 pits in a line 15 mm. long. In these specimens the rib does 

 not stand out prominently on the under side of the costal. 



Cope (Vert. Tert. Form. W'est, p. 119) identified with this species some portions of a 

 carapace found in the Bridger beds. This is here described under Amyda tequa. For a 

 discussion of the relationships of the W 7 asatch species and the closely related A. tequa of the 

 Bridger see under the latter. It is greatly to be desired that additional materials of//, radula 

 from the type locality shall soon be discovered and described. 



A. radula has the sculpture similar to that of A. cariosa. The two appear to be distin- 

 guish by the greater thickness of the shell of the latter and the groove around its free margin. 



Amyda aequa sp. nov. 

 Plate 99, figs. 1-3; text-figs. 672, 673. 



Trionyx radulus, Con , Vert. Tert. Form. West, 18S4, p. 119. 

 Amyda radulus, Hay, \iiut. Geologist, xxxv, 1905, p. 336. 



In the work above cited Professor Cope, described and referred to his Trionyx radulus, of 

 the Wasatch of New Mexico, some remains of a trionychid which he found in the Bridget beds 

 of Wyoming. This Bridger individual now belongs to the American Museum of Natural 

 History and has the number 1052. 



