NO. I LOWER EOCENE MAMMALIAN FAUNAS — GAZIN 4I 



An isolated M3 from north of Tipton Butte corresponds closely in 

 size to the above material and suggests that the beds in that area may 

 be relatively low in the Knight. 



CYNODONTOMYS KNIGHTENSIS Gazin 

 (Plate I, figure 7) 



In addition to 11 lower jaws, 4 maxillae have been added to the 

 collection representing Cynodontomys knightensis in the La Barge 

 fauna. These were obtained in 1953, 1954, and 1959, all from the 

 Muddy Creek locality 12 miles north of Big Piney, Wyo. Two of 

 the maxillae, U.S.N.M. Nos. 22106 (pi. i, fig. 7) and 22107, include 

 P*-]VP complete. P*, though smaller than in C. scottianus, exhibits a 

 slightly more constricted lingual portion than shown in the specimen 

 figured by Matthew (1915c, p. 472, fig. 42). This tooth, however, 

 shows much less disparity in size and possibly a better separation of 

 the primary cusp and tritocone (paracone and metacone) than in 

 C. latidens. The molars, moreover, exhibit a conspicuous mesostyle 

 and the hypocone on M'- and particularly M^ is well developed. 



CYNODONTOMYS SCOTTIANUS (Cope) 

 (Plate I, figure 8) 



Five lower jaws, together with portions of both maxillae of a 

 sixth individual, have been found in the New Fork beds to the east 

 of Big Piney, Wyo. The teeth in all these are fully as large as in 

 typical Cynodontomys scottianus of the Lost Cabin beds, distinctly 

 larger than in Cynodontomys knightensis, which occurs beneath the 

 Green River tongue separating the two horizons in this area. 



The maxillae above referred to (U.S.N.M. No. 221 17; pi. i, fig. 8) 

 include P^-P* on one side, as well as M^, and P*-M^ on the other. 

 P^ and P^ are simple, nearly equal teeth with partially divided roots. 

 P^ is a triangular, three-rooted tooth with a very small deuterocone 

 and no tritocone. The latter may not be significant however, because, 

 although Matthew (1915c, p. 474, fig. 44) shows the tritocone on 

 P^ of a specimen of Cynodontomys latidens, it is not invariably pres- 

 ent in Bridger Microsyops. P* is comparable in size with M^ but 

 shows a noticeably longer labial portion and a relatively narrower 

 lingual portion than illustrated by Matthew (1915c, p. 472, fig. 42), 

 This tooth is much like that in earlier C. knightensis but with a rela- 

 tively more robust primary cusp. The upper molars in U.S.N.M. 

 No. 221 17 are a little larger than in observed Lost Cabin material of 

 C. scottianus, except for a specimen in the American Museum col- 



