NO. I LOWER EOCENE MAMMALIAN FAUNAS — GAZIN 3I 



side of Oregon Buttes, is only a little larger than the New Fork 

 material referred to A^. nunienus, but seems too small for N. venti- 

 colus. The teeth can be matched for size in Bridger material of 

 Notharctus tenebrosus, and nearly matched in general form of the 

 molars, but the identity is rather uncertain and such an assignment 

 would be unwarranted. 



OMOMYIDAE 



OMOMYS SHEAI,6 new species 



(Plate 2, figures 3 and 4) 



Type.— Right ramus of mandible with M2-M3, U.S.N.M. No. 

 22384. 



Horizon and locality. — La Barge local fauna, Lost Cabin equiva- 

 lent, 12 miles north of Big Piney, Sublette County, Wyo. 



Specific characters. — Size of lower molars between Gray Bull 

 Omomys vespertinus Alatthew and Lysite Omojnys minutiis Loomis. 

 Trigonid of lower molars a little less elevated and a httle better 

 basined than in O. vespertinus. Talonid basin relatively narrower. 



Description. — Although intermediate in size between Omomys 

 vespertinus and Omomys minutus, Omomys sheai is close to O. ves- 

 pertinus and might well fall within the size range of the latter, recall- 

 ing the variation in this respect of Bridger Omomys carteri. The 

 crowns of the teeth, however, seem to be a little more advanced in 

 the direction of Omomys carteri in that the trigonids of the lower 

 molars do not appear to be as elevated on the outer sides and their 

 apices show a tendency toward distinct basining seen in Bridger 

 material. 



A second jaw portion (U.S.N.INL No. 19197; pi. 2, fig. 3) with 

 only M3, was questionably referred to Ahsarokius in 1952 (p. 24). 

 The tooth is nearly identical in size to this molar in the type of O. 

 sheai and may well represent this species. It differs only in that the 

 trigonid is slightly shorter, anteroposteriorly, and the paraconid is 

 somewhat weaker and a little more medial in position. 



Loomis's Omomys minutus (pi. 2, fig. 5) would seem correctly 

 allocated to Omomys although nothing is known of the premolars 

 of this decidedly small species. The molars exhibit high and deli- 

 cate-appearing cusps and the trigonid is rather elevated in comparison 

 with the better-known middle Eocene material. Although it has a 

 stratigraphic position intermediate between the type of 0. vesper- 



6 Named for George Shea of Billings, Mont., who graciously aided in the 

 field in 1949. 



