1890.] NATURAL SCIENCES OF PHILADELPHIA. 55 



Hycenodictis Gaudryi Hyrenodictis Filholi. 



Tricuspiodon. 



Procyonictis Proviverra. 



(Multituberculata.) 

 Neoplagiaulax eocaenus. 



" Maishii. 



" Copei. 



MESODONTA. 



Schlosser (2, p. 38) has shown that the American lower Eocene 

 monkeys are probably not lemurs, as ]Marsh and Cope have supposed, 

 because the true lemurs, with one or two exceptions, have incisiform 

 lower canines and caniniform anterior premolars ; in other words in 

 most genera, the first premolar has the function and form of a canine. 

 This important distinction renders it probable that Frotoadajyis and 

 Plesiadapis belong among the Mesodonta (Pseudolemuroidea, Schlos- 

 ser). The latter genus has a highly reduced and modified dentition, 

 with no resemblance to that of Adapts. The former has a large 

 canine and much reduced first premolar and resembles some of the 

 American forms. 



PROTOADAPIS. Lemoiue. 



P. (Plesiadapis) recticuspidens, Lem. '78, p. 14. P. (Pies.) crassicuspidens, 

 Lem. '78, p. 13. P. cti)~c'icnspidens, Lem. '78, p. 12. P. Copei, Lem. '79a, p. 7. 



Gen. char.: Dentition i; C; pi(4) mi. Inferior molars 

 quinquetubercular. The first lower premolar oc- 

 casionally present. The incisors small. The ca- 

 nines large. 



This is an older and more primitive form than Plesiadajjis as 

 shown by its fuller dentition and the retention of the paraconid 

 which completes the primitive triangle of the lower molars. These 

 teeth recall the structure seen in Microsyops among the Ameri- 

 can Mesodonta. Although belonging to an older horizon we have 

 no positive grounds for supposing that this genus is an ancestor of 

 Plesiadapis, or that either of these forms are genetically related to 

 Adapis. In fact the tendency to a rapid reduction of the premolars 

 and specilization of the incisoi's point away from Adajyis in both 

 cases. 



PLESIADAPIS, Gervais. 



P. (n'cmpidens, Gervais (3 p.). P. Re/mtisis, Lem. '87a. P. Gerfaisii,htm. 

 '87a. P. Daubreei. Lem. '87a. 



Gen. c h a r. : Dentition if c? p| mf . Median superior 

 incisor and one lower incisor enlarged, remaining 

 incisors andcanines small or wanting. Upper mo- 



