410 Wortman — Studies of Eocene Mammalia in the 



certainty be erroneous. His technical definition of the group, 

 moreover, as well as its dissociation from the Primates, I regard 

 as utterly unsound, illogical, and in no wise warranted by the 

 facts. I do not believe that any such natural group exists, and 

 a revival of the name Mesodonta can result only in confu- 

 sion. As we have already seen, there are types of very differ- 

 ent affinities among these ancient Primates, and this fact in 

 my judgment effectually precludes the possibility of their asso- 

 ciation into a single group. What position, then, do Adapis and 

 ]\ T otha? , ctus occupy with reference to these natural groups 

 already outlined ? That they can not be consistently placed in 

 the Lemuroidea is evident for the following reasons : The 

 incisors do not exhibit any traces of lemurine modification, but, 

 on the contrary, are like those in typical monkeys ; the main 

 entocarotid canal traverses the petrotympanic chamber as in 

 Tar silts ; the lachrymal and malar do not unite on the ante- 

 rior rim of the orbit ; the digital lengths of the manus are not 

 known with certainty, but in Notharctus, the evidence is rea- 

 sonably conclusive that the fourth was not longer than the 

 third. 



On the other hand, their resemblance to the Paleopithecini 

 is more marked. This is seen in the greatly inflated condition 

 of the tympanic bullae as well as in the outward and backward 

 extension of the external alse of the pterygoids. These forms 

 differ from the Paleopithecini, however, in having a more 

 reduced lachrymal, in the position of the external opening of 

 the lachrymal canal on or near the rim of the orbit, in having 

 a greater number of premolars, and in general in being larger 

 and of more robust proportions. Thus, it will be seen that 

 they occupy a position intermediate in many respects between 

 the remaining Anthropoidea and the Paleopithecini. In the 

 latter, there seems to have been a marked tendency toward 

 precocious specialization in both tooth reduction and brain 

 enlargement, which are curiously associated with retention of 

 the primitive condition of the lachrymal. Adapis and 

 Notharctus, on the other hand, exhibit advance in the reduc- 

 tion of the lachrymals, but retain the more generalized features 

 of the dentition and brain enlargement. These are the essen- 

 tial differences between the two lines and mark out very 

 distinctly the trend as well as the possibilities of their future 

 development. It is in just such a group as that which 

 includes Adapis, Notharctus, and Limnotherium, that we 

 must seek for the beginnings of the higher monkeys and 

 apes which follow ; and while these species, at present the 

 only well-known types of the series, may not have been 

 in the direct line of descent, they can not at the same time 

 have been far removed from it. Omomys and Washakius, 



