r. Robinson made
available the draft of a short paper he had prepared on the
tooth found in Weld County, Colorado; his work was
facilitated by a grant from the University of Colorado
Council on Research and Creative Work. I also gratefully
acknowledge receipt of critical data and valuable comments
from Drs. Edwin C. Galbreath, Glenn L. Jepsen, and Malcolm
C. McKenna who is currently revising the Paleocene
apatemyids and studying the phylogenetic relationships of
the family. The prefixes of catalogue numbers used in the
text identify fossils in the collections of the following
institutions: KU, Museum of Natural History, The University
of Kansas, Lawrence; Princeton, Princeton Museum, Princeton,
New Jersey; RAM-UCR, Raymond Alf Museum, Webb School of
California, Claremont, California (the permanent repository
for these specimens will be the University of California,
Riverside); and UCM, University of Colorado Museum, Boulder,
Colorado. The system of notations for teeth prescribed for
use here is as follows: teeth in the upper half of the
dentition are designated by a capital letter and a number;
thus M2 is the notation for the upper second molar; teeth in
the lower half of the dentition are designated by a
lower-case letter and a number; thus p2 is the notation for
the lower second premolar.

Family APATEMYIDAE Matthew, 1909

Genus =Sinclairella= Jepsen, 1934

=Sinclairella dakotensis= Jepsen, 1934

The type of the species, Princeton no. 13585, was discovered in
Chadronian strata of the upper part of the Chadron Formation cropping
out in Big Corral Draw, approximately 13 miles south-southwest of
Scenic, in southwestern South Dakota (Jepsen, 1934, p. 291). Detailed
descriptions of the type specimen are given in papers by Jepsen (1934)
and Scott and Jepsen (1936). Isolated teeth of Chadronian age referable
to _Sinclairella dakotensis_ have been discovered subsequently at a
locality in Nebraska and fossils of Orellan age, also referable to _S.
dakotensis_, have been collected at two localities in Colorado. The
sample from each locality is described separately.

Sioux County, northwestern Nebraska

_Material._--RAM-UCR nos. 381, left M1; 598, left m2; 1000,
right m1; 1001, right m2; 1079, right m2; 1674, right M2;
and 3013, left m2.

_Locality and stratigraphy._--These Ch