24 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.63. 



Dot require opposability of the first digits to adapt them to a perfect 

 arboreal hfe; the spreading, clawed foot being sufficient in these little 

 creatures to give a firm and secure grasp of a tree trunk or limb 

 under all conditions, just as they do for the tree-living squirrels, 

 insectivores, etc. Thus in all these forms, opposability, if it may be 

 so termed, is developed between two feet clasping opposite sides of a 

 branch, instead of between the first digit and the others of each foot. 

 The possible origin of the South American monkeys is discussed 

 more fully under the next heading. 



RESTUDY OF THE AMERICAN NOTHARCTIDS. 



Although no representative of the Notharctid group of Primates 

 appears in the Fort Union collection, the fact that certain species 

 found in these beds belong to well-developed major groups of the 

 Tarsiids, which are almost as clearly defined as their Eocene relatives, 

 makes it exceedingly probable that the Xotharctids also existed at 

 that time as a distinct group, and this fact furnishes good ground for 

 a restudy of these Primates ^^ from the viewpoint of their being a 

 much less primitive and less basic group than has been assumed by 

 Doctor Gregory. In his recent admirable and exhaustive mono- 

 graphic memoir on the subject,^* Gregory has studied in detail the 

 tooth, skull, and skeletal characters, comparing them at great length 

 with the modern Primates, and especialh' the Madagascar lemurs. 

 From this and earher studies he has concluded that the members of 

 the Notharctid group are ''true lemurs," sufficiently primitive to be 

 considered as standing near the base of the order and ''represent in 

 many respects the earliest ancestors of the higher Primates" (seep. 

 22). In this connection he writes also that "they also tend to con- 

 nect the Primates with some group of arboreal insectivores, probably 

 of the Mesozoic ancestors of the Menotyphia. " 



I can not agree with Doctor Gregory in these conclusions, either as 

 to his assumed ancestral relationship of the Xotharctinae to the 

 modern Primates or the extreme primitive stage to which he assigned 

 this group. This for two reasons, first, because of the facts stated 

 above regarding the relatively advanced condition of the major 

 groups of the Tarsiidae including those discovered in the Fort Union 

 (Paleocene), and second, because of different interpretations and 

 values which may be given to many of the morphological characters 

 exhibited in the known materials representing the Notharctid group. 



1' Since the present writer has not had for comparison at first hand any of the European Adapinae 

 material, this group has for the most part been left out of the discussion. However, it may be stated 

 that Gregorys disposition of the group, in which he follows Stehlen, regarding its relationship to the 

 Notharctinae is for the present accepted. Hence, the broader conclusions here reached regarding the 

 Notharctinae may apply equally well to the Adapinae. 



"Memoirs Amer. Mus. Xat. Hist., new ser., vol. 3, pt. 2, September, 1920 



