BAENIDA. 85 
Chisternon undatum Leidy. 
Plate 22; text-figs. 71-75. 
Baéna undata, Lewy, Proc. Acad. Nat. Sei. Phila. 1871, p. 228; U.S. Geol. Surv. Montana, ete., 1871 
(1872), p- 369. —Corr, 6th Ann. Report U. S. Geol. Surv. Terrs., 1872 (1873), p. 622; Vert. Tert. 
Form. West, 1884, p. 147, plate xix, figs. 3-5.—Osporn, Scott, and Sprer, Contrib. Mus. Geol. and 
Arch. Prinéeton Univ., No. 1, 1878, p. 96.—Hay, Bibliog. and Cat. Foss. Vert. N. A., 1902, p. 438. 
Chisternon undatum, Lerpy, Proc. Acad: ne Sei. Phila. 1872, p. 162; Contrib. Ext. Patina West. Terrs. 
1873, pp. 169, 341, plate xiv, figs. 1, 
The type of Leidy’s Chisternon undatum is in the collection of the Academy of Natural 
Sciences at Philadelphia. The specimen is said to have been collected in a range of buttes a few 
miles from Fort Bridger. This range is probably Grizzly Buttes and the lev elis B. The shell 
belonged to a turtle whose carapace had a length of about 485 mm. The front and the rear of 
the shell are missing, so that Leidy could not Pnew the structure of the bones and scutes of the 
front of the carapace. As stated by that author, the shell is rather high and archt, its upper 
surface standing above the bottom of the plastron about 7.5 inches, equal to 190 mm. The 
sutures may be fracca by means of the band of striations that crostthem, and Leidy was enabled 
to map correctly the bones of the plastron. The mesoplastra come to a point at the midline. 
The costo- marginal sulci over the bridges run about 50 mm. above the borders of the shell. 
Fics. 71 AND 72.—Chusternon undatum. Carapace and plastron. 
71. Plastron of No. 3932 A.M.N.H. X }. Anterior lobe missing. 
72. Carapace of No. 5959 A.M.N.H. x }. Areas of some bones not mapt. 
Many characters given by Cope as distinguishing this species from C. hebrarcum are not 
conclusive. There is no appreciable difference in the sizes of the anterior lobes; nor do the 
intergular and gular scutes of C. undatum always start from a common point. So far as the 
writer has observed, the marginal scutes of C, hebraicum rise considerably higher above the 
margins of the shell over the ‘bridges than they do in C. undatum. As will be shown below, 
there are important differences in the skulls. 
In the American Museum there are 4 large shells which are regarded as belonging to this 
species. In none of these are the boundaries of all the bones to be made out, altho in some of 
them many sutures may be traced. ¥ 
No. 3932 (plate 22; text-fig. 71) was collected in 1893 in the Bridger beds of Wyoming, but 
the exact locality and level are unknown. The length along the midline is 433 mm.; the 
