Marsh Collection, Peabody Museum. 401 



in its posterior border completed by the periotic, as is so fre- 

 quently, if not universally, the case in the lemurs. The 

 incisors are three above and below, and. the lachrymal canal is 

 located within the orbit. Although not positively known, it 

 is probable that the lachrymal did not have an extraorbital 

 extension. The pattern of the molars is unlike that of any 

 known Primate, but in many respects is like that of certain 

 primitive Ungulates. From several fragmentary skeletons in 

 the Marsh collection, I am now fortunately able to state that 

 the limbs were totally unlike those of the Primates. In the 

 presence of a super trochlear foramen, the humerus differs from 

 that of any known Primate. The metapodials do not display 

 the typical globular heads of those of the Primates, but are 

 depressed and strongly keeled at their distal ends. The 

 phalanges are short and stout, and give to the foot a distinctly 

 terrestrial rather than an arboreal character ; and, lastly, may 

 be noted the very important character of a completely nonop- 

 posable hallux. The North American Hyopsodidse do not, in 

 fact, possess a single Primate feature, as far as can be discov- 

 ered, but on the contrary are much more like the Insectivora, 

 to which order I refer them. A summary of the foregoing 

 characters, in which they differ from typical Primates, may be 

 given as follows : 



(1) There are three incisors above and below ; (2) there is 

 no ossified tympanic bulla ; (3) the structure of the molars is 

 not like that of the Primates; (4) the entocarotid circulation 

 is like that of the Insectivora; (5) the limb bones differ from 

 those of any known Primate; (6) the metapodials are not 

 Primate ; (7) the phalanges are short ; and (8) the hallux is not 

 opposable. 



It would appear from the evidence obtained that there are 

 no less than three distinct primary divisions of the order now 

 known, and as these represent as many subordinal groups, the 

 Primates have accordingly been divided into three sections. 



The first group which is deserving of a subordinal rank 

 among the Primates, although not commonly admitted, is that 

 represented by the living Aye Aye of Madagascar. Along 

 with this go the American Eocene genera Mixodectes, Cyno- 

 dontomys, Microsyoj)s, Smilodectes, and Metacheivomys. The 

 most distinctive and important features of this group con- 

 sist in the enlargement of the central pair of incisors, the 

 limitation of the enamel to their anterior faces in the later 

 forms, in consequence of which they wear into chisel-shaped 

 points, and, finally, their growth from persistent pulps. 

 Concomitantly, the outer incisors and canines disappear, and 

 the mandibular condyles as well as the glenoid fossae become 

 modified and adapted to a longitudinal, instead of a vertical 



