_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 Chadronian fossils were
discovered by Raymond Alf and members of his field parties
in several harvester ant mounds built in exposures of the
Chadron Formation in Sec. 26, T 33 N, R 53 W, Sioux County,
Nebraska (Alf, 1962, and Hough and Alf, 1958). This is UCR
locality V5403. The collectors carefully considered the
possibility that some of the fossils found in the ant mounds
were collected from younger strata by the harvester ants and
concluded this was unlikely (Alf, personal communication).
_Description and comments._--The cusps of RAM-UCR no. 381, a
left M1, are sharp and the wear-facets resulting from
occlusion with the lower dentition are small. The paraconule
is a low, ill-defined cusp on the anterior margin of the
crown; a metaconule is not present. A smooth stylar shelf is
present labial to the metacone. The crown was supported by
three roots. There are no interradicular crests.
The crown of RAM-UCR no. 1674, a right M2, is heavily
abraded and many morphological details of the cusps have
been destroyed. Low interradicular crests linked the three
roots of the tooth with a low, central prominence. As was
the case with RAM-UCR no. 381, no significant differences
could be found in comparisons with illustrations of the
teeth preserved in Princeton no. 13585.
RAM-UCR nos. 598, 1001, 1079, and 3013 all appear to be
m2's. The talonids of these teeth are not elongated, their
trigonids have quadrilateral outlines, and the paraconids
are small but prominent, bladelike cusps. The trigonid of
RAM-UCR 1000 is elongated and the paraconid is a minute
cusp; the tooth closely resembles the m1 of the type of
_Sinclairella dakotensis_.