82 



(iKEGORY: NOTHARCTUS, AN AMERICAN EOCENE PRIMATE 



The manus of Notharctus, (Figs. 11,83) so far as indicated by the fragmentary remains, appears to 

 be somewhat more primitive than that of any modern lemurs: (1) the unciform is not so deep vertically, 

 (2) the magnum is relatively deeper, (3) the facet for the lunar on the radius is thicker anteroposteriorly. 

 Hence, by inspection of the surrounding elements, it is probable that (4) the lunar was not so much 

 reduced as it is in lemurs, (5) the centrale probably had little if any contact with the unciform, and pos- 

 sibly (6) the poUex was somewhat less divergent. These presumably primitive characters are retained 



Fig. 11. Dorsum of riglit inaiius of Xotharrfn.'i fijrainivs. Anicr. Mus. Xo. 1147S. Xatural size. For inamis of 

 .V. osborni see Fig. S3. 



in the modern platyrrhine monkeys which, however, have also specialized in the opposite direction by 

 the further enlargement of the lunar and by the widening of the upper end of the magnum. 



The metacarpals of Notharctus are very short and most like those of the modern Perodidicus, but 

 much shorter. The long slender phalanges almost suggest those of Indris or of Chiromys rather than 

 the flattened phalanges of either the typical platyrrhine monkeys or the modern Lemurids. 



The single known ungual phalanx, which is provisionally mounted on digit IV, is strangely asym- 

 metrical. Its exact counterpart was not found in any of the primates compared with it. The nail was 

 evidently longer and narrower than those of Lemurida?, Indrisidse, Lorisida?, but not so narrow as those 

 of Chiromys. It was, however, essentially lemuroid in shape, and the ungual phalanx itself differs from 

 those of the Cebidae, which have very feeble shafts and very small round tips. 



The following additional details concerning the structure of the manus of Notharctus seem worthy 

 of record. In Notharctus osborni the manus is represented only by some of the carpals and scattered 

 elements of the digits. In Notharctus tyrannus the left hand is represented by carpals 2-5, proximal 

 phalanges 2-5, and the unciform and other fragments. The right hand is represented by the fifth meta- 

 carpal, the fourth proximal phalanx of the fourth digit, the middle phalanges apparently of the third 

 and fourth, and a single distal phalanx which may belong with the fourth. What is apparently the first 

 metacarpal is preserved in Notharctus osborni; it is similar to that of Lemur, and on the inner side of the 



