938 MONOGRAPHS OF NORTH AMERICAN RODENTIA. 
Genus COLONYMYS Marsh. 
Colonomys Marsu, Amer. Journ. Sci. and Arts, 3d ser, iv, 1872, 220, 
Known only from several isolated molar teeth of an apparently Sciurine 
character. 
COLONYMYS CELER Marsh. 
Colonomys celery Marsu, Amer. Journ. Sci. and Arts, 3d ser. iv, 1872, 220. 
About half the size of the Brown Rat (Aus decumanus). Known, like 
the genus, only from a few detached molar teeth, from the Tertiary deposits 
of Henry's Fork, Wyoming. 
Genus TAXYMYS Marsh. 
Taxynys Marsu, Amer. Journ. 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 lucaris Marsu, Amer. Journ. Sci. and Arts, 3d ser. iv, 1872, 219. 
Rather smaller than the Flying Squirrel (Sccwropterus 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 Marsu, Amer, Journ. Sci. and Arts, 3d ser. iv, 1872, 219. 
T'wo 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 senec Marsu, Amer. Journ. Sei. and Arts, 3d ser. iv, 1872, 219. 
“About the size of a rat.” Length of the lower molar series 117; 
depth of the lower jaw at the second molar 5™". Described from a lower- 
jaw fragment, having the second molar in place. The jaw is described as 
