NO. 6 TALEOCENE FAUNAS OF BISON BASIN — GAZIN 3I 



determinable species, the larger of which exhibits a surprising range 

 in size. A complex similar to that in the Bison basin picture is seen 

 in the fewer though distinctly better materials encountered in the Fort 

 Union of the Crazy Mountain field in Montana. Simpson was there 

 faced with the necessity of recognizing five species, but undoubtedly 

 this arrangement would also be somewhat simplified if an adequate 

 sample could be obtained. 



Except for the largest form in the Bison basin fauna, there seem 

 to be no characters but size by which the various species may be 

 recognized. Using Simpson's histogram (1937b, fig. 35) for the 

 length of M2 in the Torrejon materials in the American Museum, I 

 have, in figure 2, added to the number individuals in each size group 

 according to information derived from Torrejon collections in the 

 National Museum, and included a similar histogram for the Bison 

 basin teeth. In the latter, columns are extended by dashed lines in 

 instances where in the absence of Mg the size of an adjacent molar is 

 indicative of one group or another. Specific assignments made, mostly 

 tentative, are also shown. I rather supect that with further material 

 a single intermediate group will eventually be indicated where com- 

 parison is now made with C. montanensis and C. ferox, although the 

 pattern shown in the Torrejon materials would suggest great varia- 

 tion in a large species. Nevertheless, the differences between the new 

 species, C. aero genius, and that referred to C. ferox are rather marked 

 and would appear to include more than size of teeth alone. 



CLAENODON, cf. PROCYONOIDES (Matthew), 1937 

 Plate 7, figure 5 



A decidedly small species of Claenodon is represented at the saddle 

 locality by a lower jaw, U.S.N.M. No. 20630, including the molars 

 Mi-Ms, a jaw portion retaining only P2 and P3, U.S.N.M. No. 21007, 

 and an isolated M3. The proportions of the teeth in No. 20630 are 

 very close to those in the type of Claenodon procyonoides from the 

 New Mexico Torrejon. The isolated molar represents an individual 

 slightly smaller. I was unable to find any characters of significance in 

 these specimens by which the Bison basin form could be determined 

 as distinct from the earlier C. procyonoides. 



MEASUREMENTS IN MILLIMETERS OF LOWER TEETH IN SPECIMENS OF 



Claenodon, cf. procyonoides (matthew), u.s.n.m. no. 20630 



Length of lower molar series, Mi-Ma 24.0 



Mi, anteroposterior diameter : greatest transverse diameter 77:6.1 



Ma, anteroposterior diameter : greatest transverse diameter 8.0:6.7 



Ma, anteroposterior diameter : greatest transverse diameter 8.7 : 5.6 



