NEW PALEOCENE MAMMALS SIMPSON 



241 



conspecific, but more than one individual is present, and I exclude 

 all but the principal specimen from the type materiai.-^G. G. S.] 

 Collected by A. C. Silberling. 



Horizon and locality. — Locality 27, about 500 feet above the Gidley 

 Quarry, Fort Union, Crazy Mountain Field, Mont. 



Diagnosis. — Gidley: " * * * Jaw relatively long and slender, 

 especially anteriorly ; the teeth proportionately narrow transversely 

 * * * with a decided tendency to selenodonty * * *, Xhe 

 paraconid in the molars is vestigial or lacking, and P4 is submolari- 

 form * * * the heel * * * having the crescentic form of 

 that of the molars, M^iile the metaconid is large and as high as the 

 protoconid." 



Simpson: Not directly comparable with Gidleyina montanensis.*^ 

 Generically distinct from any other described lower jaws. Differing 

 from all species of Edocion in the crescentic talonid crest of P3, less 

 molariform P4, and some details in the molars, from Tetraclaenodon 

 in the talonid basin and crescent of P3, somewhat less distinct molar 

 paraconids, smoother enamel and fewer crenulations, and from 

 Protoselene in the much more molariform P3_4. Measurements in 

 milhmeters as follows: 



Family HYOPSODONTIDAE 



Hyopsodontids are very abundant in the quarry collections. The 

 most typical and common Torrejon genus, Mioclaenus, has not been 

 identified in the collection, but there is a distinctive species tenta- 

 tively referable to the Torrejon genus Ellipsodon, and there are three 

 new genera. All these, even including the species placed in Ellipso- 

 don, show a more marked resemblance to the later hyopsodontids, or 

 to the hyopsodontines as opposed to the mioclaenines, than do the 

 Torrejon forms. They thus tend in a very important way to corrob- 

 orate Matthew's union of the frequently separated supposed fam- 

 ilies Mioclaenidae and Hyopsodontidae, and they make even a sub- 

 family distinction between the two groups impractical on present data. 



" This may be the lower dentition of G. montane nsis, but this cannot be demonstrated, and there is some 

 indirect evidence against it, making even generic identity uncertain. In view of these doubts it seems 

 practical and warranted to follow Gidley and list this important form as a species. 



