Jrom the Tertiary Formation. 121 
preliminary notice of the more important specimens is included 
in the present article. 
Arctomys vetus, sp. DOV. 
Fork river. This species was only about one-third the size of 
the modern Arctomys monaz Gm., and may at once be distin- 
Measurements. 
Length of lower jaw from condyle to base of incisor, 17°75 lines. 
Antero-posterior extent of four lower molars, - ------ 6G 
Depth of lower jaw below first molar, ee eee 2 4°5 se 
The specimens on which the species is based, were found by 
. J. W. Wadsworth and the writer, in the Pliocene beds, on 
the Loup Fork, in northern Nebraska. 
Meisor, there is a second, very fine, sharp groove. The external 
front angle is rounded, and the lateral face but slightly convex. 
he premaxillary suture forms externally an obtuse angie, with 
the apex forward, near the posterior face of the incisor. 
both jaws, the incisors are deeper than wide. 
Measurements. : 
qransverse diameter of upper incisor, ---------------- 1°6 lines. 
D Mte-posterior extent, ©. <2. 2222. - =. -=++-=--- 2° . 
en ~ of skull at premaxillary suture, .-------------- sa 
Tran h of lower incisor on are of curve,---------~---- 7. = 
y verse diameter at apex, ----- Fs a wie vues one * = 
Depth of lower jaw below first molar,....---.-------- 50: ¢ 
Antero-posterior extent of first three lower molars, - - -- - 3°5 
