492 FOSSIL TURTLES OF NORTH AMERICA. 



shell. Fig 8 represents the outer portion of the fourth left costal, the figure being oriented as 

 in fig. 7. Fig. 9 presents the sculpture on ihe proximal half of the third left costal, the upper 

 end being toward the front of the animal. 



This species differs from A. beecheri in being more deprest, in having a greater proportion- 

 ate width, and in having a coarser and more irregular ornamentation. From Cope's type of 

 Aspideretes? vagans it seems to differ in having a coarser sculpture. From A . coalescens Cope, 

 as exemplified by Lambe's specimen described under the name of T ' . vagans, it differs in 

 having the carapace convex in front and in the different form of the nuchal and in the relatively 

 greater width; likewise, in possessing a greater number of neural plates and much larger 

 eighth costals. 



Aspideretes beecheri Hay. 

 Plate 90, fig. 2; plate 92, figs, i, 2; plate 96, figs. I, 2; teit-fig. 647. 



Trionyx foveatus, BAUR, Proc. Acad. Nat. Sci. Phila. 1891, p. 418. rMARSH, Monogr. U. S. Geol. Surv. 



xxvn, 1897, p. 527. 

 Aspideretes beecheri, HAY, Amer. Jour. Sci. (4), xvm, 1904, p. 274, plate xvi; Amer. Geologist, xxxv, 



1905, P- 33 8 - 



In the Marsh collection of fossil vertebrates at Yale University, there is a finely preserved 

 specimen of a trionychid to which the above name is given. It was collected in the year 1889, 

 by Prof. J. B. Hatcher and Dr. C. E. Beecher, in the Laramie beds of Converse County, 

 Wyoming, on the east side of Lance Creek. It is named in honor of one of the collectors, 

 Dr. C. E. Beecher, formerly professor of paleontology in Yale University. 



This specimen was studied by Dr. G. Baur and was identified by him as Trionyx foveatus 

 of Leidy. The present writer does not agree with this identification. Leidy's species was 

 based on scant materials, but the ornamentation of the costal bones is characteristic and has 

 led to the identification of the species by Mr. L. M. Lambe in well-preserved and complete 

 remains. These remains indicate a very different trionychid from the one here described. 



The type of A. beecheri presents the limbs nearly complete, a portion of the neck, the tail, 

 the shoulder and pelvic girdles, a large portion of the carapace, and the whole of the plastron. 

 The skull, some costals, and most of the neurals are missing. 



The carapace (plate 92, fig. i) was nearly as broad as long, the length being close to 323 

 mm.; the width 310 mm. It was apparently rather convex, but has suffered some crushing 

 during fossilization. The front of the shell, along the nuchal, was nearly straight, but at the 

 ends of this bone the border has a scallop on each side. The lateral borders are somewhat 

 sinuous. The hinder border appears to have been excavated, but here the costals are wanting. 



The nuchal has a width of 30 mm. in the midline, being somewhat notcht for the reception 

 of the preneural. Its outer end appears to project slightly over the first costal plate. The 

 preneural is of hexagonal form, 27 mm. long and 30 mm. wide. The first true neural is hexag- 

 onal, with the narrow end forward, as usual in the species of this family. It has a length of 

 32 mm. and a width of 21 mm. The second neural is of similar shape, 42 mm. long and 26 mm. 

 wide. The costals display nothing characteristic. There were probably 8 of them. The ends 

 of the costal ribs project beyond the disk about 17 mm. anteriorly, but posteriorly they are 

 longer, that of the seventh being about 50 mm., that of the eighth probably about 70 mm. 

 The costals are about 5 mm. thick along their borders. 



The sculpture of the carapace consists of a network of ridges inclosing rather deep pits. 

 Of these there are about 5 in a distance of 10 mm. Usually they are without definite arrange- 

 ment, but toward the outer ends of the costals they dispose themselves in rows parallel with the 

 margin of the shell. The bottoms of the pits are flat, and the walls rise abruptly. In Aspideretes 

 foveatus the pits have concave bottoms and the surrounding walls rise gradually. Often, too, 

 there are broad smooth spaces between the pits on the proximal ends of the costals of A ' . 

 foveatus. In A. beecheri the sutures between the costals resemble seams in leather sewed with 

 fine stitches. 



The plastron is complete. The entoplastron is slightly notcht in front. Its lateral limbs 

 include between them less than a right angle, and the length of each is 93 mm., measuring 

 from the anterior notch of the body of the bone. The epiplastra are broad at their anterior 

 ends. They resemble much those of Platypeltis mutica. The hyoplastra are not co-ossified 



