112 



BULLETIN 1G9, UNITED STATES NATIONAL MUSEUM 



tentatively removed to the Deltatheridiidae. The genus of most 

 doubtful affinities still retained in this family is XenacodonMsitthew 

 and Granger, of the Tiffany, 



The more positively leptictid genera Diacodon, Prodiacodon, 

 Leptacodon, and Myrmecoboides also occur in the Paleocene, the last 

 three being represented in this fauna. Table 23 shows some of the 

 more striking distinctions in the lower dentitions of the five genera 

 recorded from the Paleocene. 



Of these genera, Diacodon, Prodiacodon, and Lej)tacodon are typical 

 leptictids and are evidently very closely allied, to such a point that 

 they are rather difficult to distinguish. Myrmecoboides seems to be 

 a true leptictid but is liighly distinctive and perhaps not closely 

 related to any of the more typical genera. Xenacodon is a distinctive 

 but poorly known and rather dubious form. 



Genus PRODIACODON Matthew, 1929 



PRODIACODON CONCORDIARCENSIS Simpson 



Figure 14 

 Prodiacodon concordiarcensis Simpson, 1935d, p. 228. 



Type.— V.S.N. M. no. 9637, left lov/er jaw with P2, P4, M3, and 

 alveoli. Collected by Dr. J. W. Gidley. 



Horizon and locality. — Gidley Quarry, Fort Union, Middle Paleocene 

 horizon. Crazy Mountain Field, Mont. 



Figure li.— Prodiacodon concordiarcensis Simpson, U.S.N.M. no. 9637, left lower jaw: a, Crown view; 

 6, internal view. Five times natural size. 



Diagnosis. — Much smaller than Prodiacodon puercensis. P4 v/ith 

 paraconid more secant and projecting more anteriorly, talonid with 

 three conical cusps, hypoconid largest and entoconid smallest. Mj 

 with trigonid more slender and markedly elevated, talonid less 

 elongate, with three subequal cusps. 



Remarks. — P2 has a high but small paraconid and low posterior 

 cuspule. The horizontal ramus is ver}^ long and slender, and the 

 anterior teeth were evidently procumbent. 



