358 Wo7'tman — -Studies of Eocene Mammalia in the 



The type specimen was found by Professor Marsh, at Grizzly 

 Biittes, Bridojer Basin, Wyoming. The type of Mesacodon 

 speciosus was also found by Professor Marsh at the same place. 

 Other specimens are recorded from this locality ; also from 

 Dry Creek, and from Millersville. The single specimen which 

 I obtained is from the same horizon as that in which the type 

 was found. 



3Iicrosij02?s gracilis Leidy. 



Microsyops gracilis Leidy, Proc. Acad, Nat. Sci. Phila., April 16, 1872, 

 p. 20 ; Bathrodon typus Marsh, this Journal, August, 1872, p. 19, Separata ; 

 3Iicrosyo2:>s typus Osborn, Bull. Amer. Mus. Nat. Hist,, 1902, p. 212, 



As already noted, Leidy, in his final description of M. gra- 

 cilis, believed it to be the same as M. elegans. This is 

 undoubtedly true of the first specimen mentioned, but a second 

 lower jaw was associated with the latter, with the expression 

 of some doubt as to its specific identity. There are in the 

 Marsh collection four specimens, exclusive of the type of Bath- 

 rodon typus, figure 113, consisting of the upper and lower 

 jaws of a form which agrees in every way with the figures and 

 descriptions given by Leidy of his second specimen. These 

 are supplemented by three more examples of upper teeth 

 obtained by myself in the type locality last summer. The 

 additional material enables me to determine that this series of 

 specimens is not only larger than the typical M. elegans, but 



113 



Figure 113. — Lower jaw of Microsyops gracilis Leidy (type of Bathrodon 

 typus Marsh) ; viewed from above ; two and one-half times natural size. 



Figure 114. — JJpfTer jaw of Microsyops gracilis Leidy; crown view; 

 twice natural size. 



presents other constant differences which I think impossible to 

 account for on the basis of differences in age or sex. In.no 

 case are the upper teeth, figure 114, associated with those of 

 the lower jaw, but as in tiie preceding species, the size and 

 character of the two correspond so closely that there can be 

 virtually no doubt of their relations. The more important 

 distinctive characters are the following : The teeth are slightly 

 larger than those of 2L elegans, and the jaw is appreciably 

 heavier and deeper ; the last upper molar has a distinct meso- 

 style and a posterior intermediate cusp, both of which are 

 absent in the same tooth of M. elegans ; the fourth superior 

 premolar has a mesostyle and the posterior intermediate dis- 



