450 Bulletin American Museum of Natural History. [Vol. XXXIV, 
Specific characters: Mi3=5 mm. Size of the Bridger species Omomys ameghint 
Wortman, but teeth narrower and paraconid more distinct, if Wortman’s figure be 
accurate. 
Through courtesy of Dr. Loomis I have been able to study this interest- 
ing little type which is unlike anything in the American Museum collections. 
The species agrees with Omomys in the construction of the molars, and in 
the slender jaw with premolar roots indicating that these teeth were of 
moderate width and not crowded. It is much smaller than O. vespertinus 
infra. 
2?0momys vespertinus sp. nov. 
Type, No. 16835, lower jaw with mi_;, from Upper Gray Bull beds at head of Elk 
Creek in the Bighorn basin, Wyoming. 
Paratype, No. 16213, upper jaw with p*-m? from top of Almagre beds, San Juan 
basin, New Mexico. | 
Specific characters: Mi_3=7.8 mm. Size of O. cartert but last molar smaller and 
paraconid on me; more internal in position and partly connate with metaconid. 
This species is very doubtfully referable to Omomys, the lower molars 
being intermediate in character between that genus and Tetonius. They 
have the low crowns and comparatively narrow proportions of Omomys, 
3 No. 16835 
4 A./”. 
Fig. 22. Fig. 23. 
Fig. 22. Omomys vespertinus, lower jaw, outer view, and crown view of teeth. Type 
specimen, upper Gray Bull beds, Bighorn basin, Wyoming. 
Fig. 23. Omomys vespertinus, upper jaw, outer and crown views. Paratype, top of 
lower (Almagre) beds of Wasatch, San Juan basin, New Mexico. 
with small trigonid of less width than talonid; and the last molar is but 
little reduced. The position of the paraconid agrees better with Tctonius. 
The premolars and front teeth are unknown. 
A well preserved jaw from the New Mexico Wasatch accords in size and 
proportions with the type, and is likewise of somewhat intermediate charac- 
ter although the relationship to Omomys is more evident. The last molar 
2 slightly reduced but shows, like the others, the characteristic trigonal 
