1902.] Osborn, American Eocene Primates. 203 



Part II. Rodentia. 

 Suborder PROGLIRES, subordo nov. 



A primitive suborder of Rodents distinguished by the presence of 

 rooted incisors, and canine teeth, and by the absence of any consider- 

 able diastemata and of antero-posterior motion of the jaw. Types: 

 Mixodectes, Olbodotes, Microsyops. 



It is obvious that these animals are far too primitive to 

 be classed with the Protrogomorpha of Zittel which was framed 

 to include all those inodernized fossil and living rodents which 

 do not naturally enter either of the four great divisions of 

 Brandt. 



Family MIXODECTID^ Cope. 



Characters .—Me6\Sin lower incisors close to symphysis, enlarged and 

 elongating (unlike Tillodontia, in which second incisor is enlarged), 

 lateral incisors early reduced; canines persistent (unlike Rodentia); 

 no diastemata (unlike Rodentia) , first and second premolars rapidly 

 reduced; third premolar slowly reduced, fourth premolar progressively 

 molariform (as in Tillodontia and Rodentia) ; lower molars with nar- 

 row, slightly elevated trigonid, but early reduced paraconid; talonid 

 broad, hypoconulid small, except in third lower molar; superior molars 

 tritubercular. A feature of the jaw is the sharp definition of a ridge 

 descending from the coronoid and defining the masseteric insertion 

 anteriorly (Fig. 3). 



This phylum specialized very early.' The little animals 

 which represent it are rare in the Torre j on and Wasatch, 

 more abundant in the Wind River, and very common in the 

 Bridger; not as yet reported in the Uinta. The specific 

 forms range greatly in size but the essential progressive 

 characters of the lower teeth are the same throughout this 

 long geological period. 



Ordinal, position. — Cope placed Mixodcctes among the 

 Primates. Matthew ('97, p. 265) was the first to point out 

 that the enlarged median tooth was probably an incisor and 

 that the astragalus was exactly similar to that of a Rodent. 

 He therefore took the important step of transferring this 



' In 1892, Schlosser (Neues Jahrb. f. Min. Geol. u. Pal., Bd. II, s. 238) referred the 

 contemporary Cernaysian Plesiadapidae, Plesiadapis and Protoadapis Lemoine, to the 

 Rodentia, removing them from the Insectivora. 



