1885. ] Eocene Period of North America, 459 
acute claw is known. This alone does not decide the question, 
since such a claw exists on the second toe of many Lemuroidea. 
These animals are readily distinguished into three divisions or 
families by the number of their premolar teeth. There are four 
such teeth in the Adapide; three in the Mixodectide, and two 
in the Anaptomorphide. In the Adapidze we have the most 
primitive type, and the one most nearly allied to the Condylar- 
thra, from which they were probably derived. In the Mixodec- 
tide we have the dental formula of the existing lemurs, with a 
tendency in some of the genera to develop large cutting teeth in 
the position of incisors, thus approaching the aye-aye. In 
the Anaptomorphide, on the other hand, we find a dental for- 
mula like that of the Simioidea and Anthropoidea, or higher 
E ZZ 
` FIG. 1.—Adapis parisiensis Cuv., skull nat size, from the Phosphorites of Central 
France. From Filhol. 
monkeys and apes; and in them we seem to geta hint of the 
derivation of these higher forms, and of man himself. 
The genera of the Adapidz are distinguished by various den- 
tal characters. Such are the presence of a second anterior-inner 
cusp of the inferior true molars; the presence of an internal cusp 
of the fourth inferior premolar; the number of incisor teeth, and 
number of single-rooted premolars. The difference between the 
quadrituberculate and the quinquetuberculate inferior molar may 
be understood by reference to Fig. 2, where the teeth of the gen- 
era Hyopsodus (a) and Microsyops (2), which represent the two 
, are placed side by side. : 
oe (Notharctus, Tomitherium, Figs. 4-5) the fifth 
cusp is present but weak. In others (Sarcolemur) it is repre- 
