8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I3I 



resemblance between sites or further emphasize dissimilarities. Un- 

 doubtedly certain missing forms would appear, increasing the num- 

 ber of genera and species common to two or more localities, but better 

 representation of populations of each would likely point out per- 

 sistent differences. 



A stratigraphic difference seems evident between at least three of 

 the four sites so that differences due to environment or facies would 

 not be unexpected, whereas this would be unlikely were the same 

 horizon represented at each in so restricted a geographic area. Chance 

 collecting may be appealed to as distorting the picture with respect to 

 environmental differences, particularly where the numbers of speci- 

 mens are small ; nevertheless, with the same collecting personnel in- 

 volved at each of the sites, attention may be directed to certain con- 

 trasting features observed. The saddle locality for example shows 

 evidence of a fauna containing a wealth of smaller mammalian forms. 

 Scant numbers of specimens show a variety of multituberculates, 

 marsupials, and insectivores not represented at the other localities. 

 Still better materials include representation of primates, creodonts, 

 and condylarths, with equivalent or closely related forms known at 

 the other levels. Almost all the genera here peculiar to the saddle 

 locality, with the exception of Bisonalveus and Protoselene?, are else- 

 where known in later faunas, so that one may postulate in addition 

 to time an environmental difference possibly only of local significance 

 which, were it not for the persistence of the primates, would suggest 

 a more open or less sylvan environment for the later levels. The 

 saddle genera missing from the higher levels I suspect are forest- 

 dwelling types. On the other hand, all but two, Dissacus and Tifa- 

 noides, of the genera known in the four faunas as a whole are rep- 

 resented in the saddle collections, indicative of a cosmopolitan 

 assemblage of a type perhaps better known only from the Crazy Moun- 

 tain Fort Union and evidently also from the Polecat Bench. In all 

 probability the Torrejon fauna is of a more open terrain, although 

 points of resemblance are seen in the Carnivora. Nevertheless, the 

 condylarths in particular and many of the other forms from the Bison 

 basin seem more closely allied to faunas of the Crazy Mountain Fort 

 Union as well as to those of the Polecat Bench series. No doubt much 

 of this resemblance is regional in significance and perhajis generally 

 characteristic of the extensive Fort Union, which the Wyoming as 

 well as the Montana sites have been regarded as representing. These 

 in turn are geographically remote with a rather distinctive differ- 

 ence in latitude from the Nacimiento deposits in the San Juan basin 

 of New Mexico. 



