204 Wortman — Studies of Eocene Mammalia in the 



the Tarsius stage, figure 136. This is seen in the continuation 

 of the cingulum forward, around the internal face of the crown, 

 and the development of a distinct (singular cuspule internal to 

 the main antero internal cusp. In the two external roots of 

 the fourth superior premolars, however, the species of the 

 Omomyinse, as far as known, agree with 2'arsms. This is 

 very probably a generalized character, also, since there is very 

 strong presumptive evidence that the single external root of 

 the third and fourth premolars, common in the higher apes, is 

 the result of degeneration caused by the shortening of the face.* 



137 



138 



Figures 137, 138. — Upper and lower teeth of Cebus apella ; crown view ; 

 three halves natural size. 



The final determination of the exact relations of these forms 

 to Tarsius must await the discovery of the lachrymal region, 

 as well as of the structure of the limbs and feet. 



It is proper, however, to call attention in this connection to 

 some striking resemblances which this group exhibits to certain 

 of the South American apes, notably the capuchins and squirrel 

 monkeys. In the former of these, of which Cebus apella, 

 figures 137 and 138, is a good example, the upper molars pre- 

 sent a characteristic and in many respects a peculiar and dis- 

 tinctive pattern. The first molar is the largest of the series 



* In Cebus the external root of the third and fourth premolars is either 

 deeply grooved or completely divided at the end. This is likewise true of 

 Mycetes, as well as of many species of Old World apes. An example of th« 

 fusion of the external roots is seen in the last molar of many species of apes 

 where it is strongly reduced, as in Cebus, Chrysothrix, and others. 



