1902.] 



O shorn, American Eocene Primates. 



21 I 



Fig. 38. Microsyops. Princ. 

 Mus. Superior molars, iso- 

 lated. 



It is probable that the types of Palceacodon verus Leidy, 

 Mesacodon speciosus Marsh, Bathrodon annectens Marsh, also 

 belong to this genus. The species 

 PalcBacodon vagus Marsh apparently 

 belongs with the Anaptomorphidae. 



Leidy chose a rather uncharacteris- 

 tic specimen ' as the type and first 

 adopted the specific name M. (Hy- 

 opsodus) gracilis Marsh; ^ but as the 

 type of the latter species (H. gracilis) 

 has four premolars it is probably 

 related to Notharctus ( ?Liinnotherium) 



elegans, as in fact suggested by Leidy himself (1873, p. 84). 

 We are unable at present to straighten out the names of the 

 Bridger formation species; they appear to be numerous. 



Principal Characters of Microsyops. — y, y. ?■ 3 : median incisors very- 

 large, semi-procumbent, laterally compressed; P4 submolariform; 

 mj with small third lobe: symphysis not coossified. 



The fourth premolar of Microsyops presents an advance 



upon that of Cynodontomys 

 in the presence of a ridge 

 uniting the two anterior cusps ; 

 the incisors were still larger 

 and more procumbent, ex- 

 tending well back, below and 

 inside of the fangs of the 

 canines (Fig. 39). The ex- 

 ternal cingulum of the upper 

 molars is not constant, some- 

 times faint; the valleys are 

 smooth or slightly ridged. The 

 upper molars (Fig. 38) are 

 tritubercular, the primitive 

 cusps (protocone, paracone, 

 metacone), when unworn, be- 

 ing sharp and prominent ; the 

 conules faintly developed on m' and m'^ ; the hypocone is a 



Fig. 39. Microsyops. Am. Mus. No. 

 1732. ^, external, ,-J', internal aspect of 

 right ramus. 



' Leidy '73 pi. vi, figs. 14, 17. 



Amer. Jour. Sci., July, 1871, p. 10. 



