204 Bulletin American Museum of Natural History. [Vol. XVI, 



genus to the Rodentia, leaving the position of the more recent 



members of the family undetermined. 



Relationship to the Rodentia is now found to be indicated by : 



(i) progressive elongation of median incisor; (2) disappear- 

 ance of lateral incisors; (3) reduction 

 of canines ; (4) disappearance of two 

 anterior premolars and reduction of 

 third premolar ; (5) transformation of 

 fourth premolar into molar form, thus 

 foreshadowing a homodont molar- 

 premolar series; (6) width and ex- 

 tension of talonid (as in Eocene 

 Paramys); (7) rodent form of as- 

 tragalus. 



Against the Rodent relationship are: 

 (i) Persistence of the canine; (2) 

 absence of diastemata; (3) absence 

 of any evidence (except the levelling 

 of the premolars) of adaptation for 

 antero-posterior or orthal motion of 

 the jaw. Pending the final demon- 

 stration of this problem the Mixo- 

 dectidae may be placed in the new 



primitive suborder Proglires, defined above. 



A careful reexamination of all the material belonging to 



Mixodectes, Cynodontomys , and Microsyops has confirmed 



Matthew's observation that the enlarged median tooth is an 



incisor and has convinced us that these animals represent 



three successive stages in the same family. 



A still more primitive stage is represented by a new genus 



to which the name Olbodotes (oA/3o8oTr;s) may be given, in 



reference to the happy solution it affords of the problem of 



the homology of the enlarged incisor teeth. 



SYNOPSIS OF GENERA. 



TORREJON. 



Olbodotes. — g, y, ^, g. One enlarged and two reduced incisors; two 

 premolars, fourth premolar pointed ; depressed paraconid on the molars. 



Fig. 28. Mixodectes pungens. 

 Am. M us. No. 2451. Left femur. 

 Natural size. Astragalus, A , pos- 

 terior ; ^ ', anterior ; A ', inferior 

 or distal aspect. Natural size. 



