FORT UNION OF CRAZY MOUNTAIN FIELD, MONT. 



213 



Remarks. — As the specimen is preserved there is a small tooth 

 anterior to Mi that has been cemented to the specimen without any 

 clear or certain contact. Knowing the care with which Dr. Gidley 

 worked, I have no doubt that this tooth was found with the specimen, 

 but not knowing his exact evidence of association I am not certain 

 that it is in fact P4 of this individual. It is, furthermore, somewhat 

 incomplete. It appears to be a very small and simple tooth with a 

 short, high, conical main cusp and a single conical posterior cusp. If 

 these are its true characters, it is very much unlike P4 in any species 

 certainly referred to Didymictis, but this is too uncertain to draw any 

 conclusion, and the lower carnassial is sufficiently Didymidis-like to 

 leave the species in that genus at least until better material is found. 



DIDYMICTIS HAYDENIANUS Cope. 1882 



Figure 59 



U.S.N.M. nos. 6143 and 6145, each including an upper P*, represent 

 a species inseparable from Didymictis haydenianus. Their most 

 reliable dimension, the (oblique) 

 length of the straight shearing edge, 

 is 10.7 and 9.7 mm, respectively. 

 In Torrejon specimens referable to 

 D. haydenianus this dimension is 

 9.2-1 1 .3 mm. No constant morpho- 

 logical difference is seen. The ma- 

 terial is inadequate to establish 

 definitely that the Fort Union form 

 is exactly the same as that from the 

 Torrejon, but obviously it is not 

 separable. 



In the American Museum collec- 

 tion there is a specimen from Loc. 

 81 with broken P* and M^ The 

 oblique length of the shearing crest 



cannot be measured exactly, but it was about 11.2 mm near the 

 known upper limit for D. haydenianus. The specimen is more robust 

 than the two mentioned above and might be a large variant of the 

 same form or a different subspecies or species. 



There is also a fragment of a P4, including the heel, U.S.N.M. no. 

 9930, from Loc. 51, that has the size and cusp structure of D. hay- 

 denianus, quite unlike D. microlestes. 



Genus ICTIDOPAPPUS Simpson 



Ididopappus Simpson, 1935d, p. 237. 



Type. — Ididopappus mustelinus Simpson. 



Distribution. — Middle Paleocene, Fort Union, Montana. 



Figure 59.— Didymictis haydenianus Cope, re- 

 ferred specimens from the Lebo: a, U.S.N.M. 

 no. 6145, left upper jaw with carnassial, crown 

 view; a', same, external view; 6, U.S.N.M. no 

 6143, right upper carnassial, crown view; 6' 

 same, anteroexternal view; b", same, postero 

 internal view in outline with wear surface cross- 

 hatched. Natural size. 



