14 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I3I 



Cf. ANCONODON RUSSELLI (Simpson), 1935 

 Plate I, figure 4 



Anconodon russelli may be represented by a fragment of the right 

 mandibular ramus showing the root portion of the incisor and P4, 

 U. of Wyo. No. 1065. The preserved premolar is close in size to that 

 referred above to Ectypodus haseni, but its profile is slightly more 

 convex dorsally and has a long straight front edge more as in An- 

 conodon. P4 is 5.2 mm. in length, which is about midway in the 

 range of 4.9 to 5.4 mm. given by Jepsen (1940, p. 291) for Anconodon 

 russelli. The number of serrations is not certainly determined but 

 would appear to be about 13 or 14. Fourteen serrations are noted for 

 several of the Gidley Quarry specimens from the Crazy Mountain 

 Fort Union, but 15 or 16 prevail in the Rock Bench material accord- 

 ing to Jepsen. 



Marsupialia 



DIDELPHIDAE 



PERADECTES ELEGANS Matthew and Granger, 1921 



Plate 2, figure 6 



A rather well preserved right mandibular ramus with the posterior 

 three molars, U. of Wyo. No. 1104, corresponds so closely in direct 

 comparison with the type of Peradcctes clegans from the Tiffany of 

 Colorado that there seems no doubt that the species are the same. 

 Lower molars are, of course, amazingly conservative in didelphids, 

 but the near identity in various measurements of the teeth in the Bison 

 basin jaw and the type leave no alternative but recognition of this 

 species in the upper Paleocene of Wyoming. Measurements of the 

 teeth have been incorporated below with those of the following species 

 believed to be distinct. 



PERADECTES PAULI,^ new species 

 Plate 2, figures 4, 5 



Type. — Portion of left mandibular ramus with last two molars, 

 U.S.N.M. No. 20879. 



Horizon and locality. — Bison basin Tiffanian, saddle locality, below 

 south rim of Bison basin, sec. 28, T. 27 N., R. 95 W., Fremont 

 County, Wyo. 



Specific characters. — Appreciably smaller teeth than Pcradectes 

 elegans and lower molars with outer cusps slightly less elevated and 

 talonids relatively more abbreviated. 



2 Named for Paul O. McGrew. 



