938 MONOGRAPHS OF NORTH AMERICAN RODENT1A. 



Genus COLOXYMVS Marsh. 



omys Marsh, Amer. Jonrn. Sci. and Arts. 3d ser. iv, 1872, 220. 

 Known only from several isolated molar teeth of an apparently Sciurinc 



character. 



COLONYMYS CELER Marsh. 



Colonomys ccUr Marsh, Amer. Jonrn. Sci. and Arts, 3d ser. iv, 1872, 220. 



Alionl hall' the size of the Brown Rat (Mus decumanus). Known, like 

 the genus, only from a few detached molar teeth, from the Tertiary deposits 

 of Henry's Fork, Wyoming. 



Genus TAXYMYS Marsh. 



Taxymys Marsh, Amer. Jonrn. Sci. and Arts, 3d ser. iv, 1872, 219. 



Apparently allied to the true Squirrels, but too imperfectly known to 

 admit of characterization. 



TAXYMYS LUCARIS Marsh. 



Taxymys luearis MARSH, Amer. Joum. Sci. and Arts, 3d ser. iv, 1872, 219. 



Rather smaller than the Flying Squirrel (Sciuropterus volucella). De- 

 scribed from a portion of an upper jaw, with the first two molars in place, 

 and from a vertebra supposed to belong to the same animal. First upper 

 premolar very small, as in the Arboreal, Flying, and Ground Squirrels, with 

 a similar conformation of the triturating surface. From Tertiary deposits, 

 Henry's Fork, Wyoming. 



Genus TILLOMYS Marsh. 



Tillomys Marsh, Amer. Joiirn. Sci. and Arts, 3d ser. iv, 1872, 219. 



Two species, differing mainly in size, are referred to this genus, described 

 from very unsatisfactory fragments of lower jaws. Very little is known 

 respecting the characters of the group. 



TILLOMYS SENEX Marsh. 



Tillomys stnex Marsh, Amer. Jonrn. Sci. and Arts, 3d ser. iv, 1872, 219. 



"About the size of a rat.'' Length of the lower molar series ll mm ; 

 depth of the lower jaw at the second molar 5 mm . Described from a lower- 

 jaw fragment, having the second molar in place. The jaw is described as 



