40 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I44 



served. Some of the bone is missing along the lower part of the jaw, 

 exposing the root portion of the enlarged incisor. The jaw is rather 

 close in size to contemporary material of Phenacolemur praecox from 

 the Bighorn Basin and may be tentatively referred to this species. It 

 does, however, show differences worthy of comment. The trigonid 

 of M2 seems a little narrower and the protoconid and metaconid are 

 more conical and less developed as a transverse crest. Also, the 

 talonid basin is slightly longer and shallower, and there is less of a 

 notch anterior to the entoconid. Although these and certain other re- 

 lated features seem rather important, there would appear from Simp- 

 son's discussion (1955) to be considerable variation in Gray Bull 

 materials included in P. praecox. Should it be demonstrated, how- 

 ever, that the distinctive features of the Bitter Creek specimen were 

 persistent in a larger sample, their significance might be on a generic 

 level. 



MIXODECTIDAE 



CYNODONTOMYS ANGUSTIDENS Matthew 



(Plate I, figure 6) 



Cynodontomys material from the lower part of the Knight mem- 

 ber near Bitter Creek Station includes a maxilla with M^ and M^ 

 (U.S.N.M. No. 22121) and a lower jaw with Mi and M2 (U.S.N.M. 

 No. 22446) collected by Smithsonian Institution parties and, in addi- 

 tion to a couple of isolated teeth, a lower jaw with P3-M3 (Y.P.M. 

 No. 14696) collected by Marsh's party. These specimens seem almost 

 certainly to be of Cynodontomys angustidens described by Matthew 

 on Gray Bull Material. 



The upper molars in U.S.N.M. No. 22121 (pi. i, fig, 6) lack the 

 mesostyle seen in later species, although the external cingulum rises 

 slightly at about this position. M^ is very much like that in the speci- 

 men of C. angustidens figured by Matthew (1915c, p. 477, fig. 48) 

 but is somewhat smaller and exhibits a slightly weaker hypocone. 



The fourth premolar of the lower series in the Yale specimen is 

 a little broader than in the type of C. angustidens and shows a mod- 

 erately well-developed metaconid that is rather close to the protoconid 

 and not as high. It is, however, a little higher and more widely sepa- 

 rated from the protoconid than in the type. The talonid of P4 has a 

 decidedly narrow basin but exhibits a distinct hypoconid and en- 

 toconid. There appears, however, to be no evidence for a hypoconulid. 

 The lower teeth in Y.P.M. No. 14696 are distinctly smaller than in 

 the type of Cynodontomys latidens and the metaconid of P4 is not 

 as large and upstanding. 



