4 88 



FOSSIL TURTLES OF NORTH AMERICA. 



Small, shallow, rounded depressions mark the surface of the neurals and the inner ends of the costals. 

 In the latter, as the distance from the neurals increases, the depressions gradually grow larger and more 

 decided, becoming often reniform or oval, and frequently coalescing, until in the distal ends of the costals 

 a few more or less continuous furrows are formed parallel to the outer margins of the plates. These 

 furrows are a conspicuous feature in the sculpture; they are not so well marked on the posterior margin 

 of the carapace, but are well developed near the front edges of the first costals. In the neurals and 

 inner halves of the costals there is a narrow, smooth strip, devoid of all sculpture, bordering the sutures. 



None of the plastral bones referred by Lambe to this species were associated with the 

 carapace described. The author referred to states that the plastral bones belonged to individuals 

 of larger size than that to which the carapace belonged. A comparison of the bones with 

 corresponding parts of individuals belonging to Platypeltis ferox and P. spinifera shows that 

 the individual represented by the carapace may have been as large as the others or even larger. 

 In form the plastron (plate 89, fig. 2; text-fig. 644) resembled much that of the living 

 species just mentioned. The sculpture consists of ridges and intervening furrows of varying 



length and of irregular direction. 

 Of the ridges there are about 9 

 in a line 20 mm. long. On the 

 outer ends of the bones the ridges 

 run parallel with the long axis of 

 the animal. On the inner half, 

 the ridges are shorter, less eleva- 

 ted, and irregular in their course. 

 In the collection of fossil verte- 

 brates made in the Judith River 

 basin by Mr. C. H. Sternberg, in 

 1876, for Professor Cope, there 

 are many fragments of costal 

 bones which belongtothisspecies; 

 but they throw no additional light 

 on it. 



From the Laramie beds at Hell 

 Creek, Montana, Mr. Barnum 

 Brown has brought to the Amer- 

 ican Museum of Natural History 

 fragments of a trionychid that 

 resemble very closely similar fragments from the Judith River basin. Three consecutive 

 neurals and portions of costals have the number 1017. Had they been found in Judith River 

 deposits they would without hesitation be referred to A. foveatus. Perhaps only the finding 

 of a complete shell of this Laramie form will settle the questions involved. 



The character of the sculpture, especially that of the central regions of the carapace, 

 distinguishes A. foveatus from any other of the Judith River species with which it is likely to 

 be compared. 



The specimens of Trionyx foveatus cited by Prof. O. C. Marsh as having been found in 

 the Ceratops beds near Denver, Colorado, belong probably to Aspideretes beecheri; but the 

 present writer has not seen the materials on which Marsh's statement was founded. 



Aspideretes coalescens (Cope). 

 Plate 88, fig. 6; plate 90, fig. i; text-fig. 645. 



Plastomenus coalescens, COPE, Proc. Acad. Nat. Sci. Phila. 1875, P- 9 ( no description); Brit. N. A., 

 Bound. Comm. Report on Geol. and Resources 49th Par., 1875, P- 337> Vert. Cret. Form. West, 

 1875, pp. 93, 261, plate viii, figs. 6, 7. LAMBE, Ottawa Naturalist, xin, 1899, pp. 68, 70; Summary 

 Report Geol. Surv. Canada, 1898 (1899), p. 182-190. HATCHER, Bull. U. S. Geol. Surv. No. 257, 

 1905, p. 74. 



Trionyx vagans, ?CopE, Bull. U. S. Geol. Surv. Terrs., m, 1877, p. 573. LAMBE, Contrib. Canad. Pal- 

 aeont., in (4 to), 1902, p. 36, plate i, figs. 3, 4, text-fig. 3. 



Trionyx coalescens, HAY, Bibliog. and Cat. Foss. Vert. N. A., 1902, p. 454. 



Plastomenus (Trionyx) coalescens, OSBORN, Contrib. Canad. Palaeont., Ill (410), 1902, pp. 12, 16. 



FIG. 644. Aspideretes foveatus. Right hyoplastron and hypo- 

 plastron. X |. Reduced from Lambe's figure. 



hpo, hyoplastron; hypo, hypoplastron. 



