BAENID^E. 



85 



Chisternon undatum Leidy. 

 Plate 11; text-figs. 71-75. 



li,i, na uniata, Leidy, Proc. Acad. Nat. Sci. Phila. 1871, p. 22S; U. S. ( leol. Surv. Montana, etc., 1871 

 (1872), p. 369. Cope, 6th Ann. Report U. S. Geol. Surv. Terrs., 1872 (1873), p. 622; Vert. Tert. 

 Form. West, 1884, p. 14;, plate xix, tigs. 3-5. Osborn, Scott, and Spier, Contrib. Mus. Geol. and 

 Arch. Princeton Univ., No. I, 1878, p. 96. Hay, Bibliog. and Cat. Foss. Vert. N. A., 1902, p. 438. 



Chisternon undatum, LeIDY, Proc. Acad. Nat. Sci. Phila. 1872, p. 162; Contrib. Ext. Fauna West. Terrs. 

 1873, pp. 169, 341, plate xiv, figs. I, 2. 



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 Bridget. This range is probably Grizzly Buttes and the level is 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 know 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 traced by means of the band of striations that crost them, 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. 



Figs. 71 AND 72. CJusternnn undatum. Carapace and plastron. 



71. Plastron of No. 5932 A. M.N.H. X :}. Anterior lobe missing. 



72. Carapace of No. 5959 A. \l. \. H. ,',. Areas of some bones not inapt. 



Many characters given by Cope as distinguishing this species from ('.. hebraicum 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 met the bridges than thev 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 our, altho in some of 

 them many sutures mav be traced. 



No. 3932 (plate 22; text-tig. 71 1 was collected in 1893 in the Bridget beds of Wyoming, but 

 the exact locality and level are unknown. The length along the midline is 43^ mm.; the 



