238 BULLETIN 169, UNITED STATES NATIONAL MUSEUM 



variants with one locality or the other and possible differences in 

 mean dimensions have been carefully compared. The greatest differ- 

 ence in mean dimensions is only 0.2 mm (for width of P3), wliich is 

 not shown to be significant (it being mathematically demonstrable 

 that a difference as great would arise in random sampUng of a homo- 

 geneous sample about once in 20 trials or oftener). The other differ- 

 ences are far from any probable significance. Only one specimen 

 from the Silberling Quarry falls outside the observed range for the 

 Gidley Quarry in a single dimension, having Mi 3.8 mm in length, 

 but this is far within the probable range of the Gidley Quarry popu- 

 lation, the deviation being only 1.4 times the standard deviation. 



It is unnecessary to give the results of the numerous other detailed 

 comparisons made, since all were negative, showing no significant 

 difference between the samples from the two quarries. Since the 

 samples are so good, this warrants the positive affirmation that a 

 single race of this species occurs in both quarries. 



A single specimen from Loc. 51, U.S.N.M. no. 9709, a lower jaw 

 with Ml and broken M2, has these two teeth above the average size 

 for the Gidley Quarry sample, but within the range of the latter. 



ELLIPSODON species 



U.S.N.M. no. 9662, from Loc. 18, is a partial right lower jaw with 

 P4. This tooth resembles that of Ellipsodon aquilonius but is rela- 

 tively higher, the paraconid is more distinct, and the length, 4.2 mm, 

 is significantly greater than in that species (d/a-=4.9), although the 

 width, 2.6 mm, is not (d/a-=2.5). Tliis is probably another species, 

 but the material is inadequate for its exact determination. 



Genus LITALETES Simpson 



Litaletes Simpson, 1935d, p. 242. 



Type. — Litaletes disjundus Simpson. 



Distribution. — Middle Paleocene, Fort Union, Montana. 



Diagnosis. — P4 with bladelike main cusp, distinct paraconid and 

 relatively large metaconid, talonid small with narrow, rudimentary, 

 open basin. Molar paraconids distinct, small, internal. Entoconids 

 indistinct, fusing with hypoconulids, especially on M2. P* with rudi- 

 mentary metacone, strong metastyle. M^-^ with distinct hypocones. 

 M^3 not reduced, M^ with strong metacone. 



Discussion. — This genus is very distinct from Ellipsodon, but 

 Litaletes disjundus and Ellipsodon aquilonius do not differ very 

 greatly. It could hardly be supposed that Ellipsodon inaequidens, 

 type of that genus, is congeneric with Litaletes disjunctus, for their 

 whole adaptive tendency seems different, and each tooth has definite 

 and pronounced structural distinctions. The question then is not 

 whether Ellipsodon and Litaletes fire distinct genera, but where the 



