80 



GREGORY: AWPHARCTUS, AN AMERICAN EOCENE PRIMATE 



The marmosets vary considerably in the length of the radius. The longer straighter radii distinctly 

 suggest the Callithrix-Cebus type; the shorter radii have the shaft curved about as much as it is in Notharc- 

 tiis, but they have the styloid process shaped more as it is in Cebus. The head of the radius is circular 

 rather than oval and its outer rim does not protrude so much as it does in Nothardus. 



Comparative Measurements 





N . osbomi 



N . tyranrim 



L. mongnz 



L. mongoz 



L. variua 





No. 11474 



No. 11478 



No. 22886 



No. 31254 



No. 18040 



Total Length of Radius from distal to proixmal 













articular facets 



()7 . 



()7 (est.) 



S7. 



S.J. 



98. 



Greatest Trans\'erse Diameter of Head of l{aili\is 





7.3 





(i.S 



10. 



Greatest Width of Distal End of Radius across 













articular facets 





9.7 



8. 



7.9 



11 . 



Ulna 

 Text Fig. 10 



The ulna is represented by the right and a portion of the left in N. osborni, Amer. Mus. No. 11474, 

 and by the right in N. iyrannus (No. 11478). The chief difference from Lemur and Lepilemur is the short- 

 ness and marked curvature of the shaft; they also have the posterior border wider and flatter. The 

 great sigmoid notch is similar to that of Lemur mongoz, but somewhat less expanded transversely, in 

 correlation with the relative narrowness of the humeral trochlea; it is confluent with the small sigmoid 

 cavity for the reception of the head of the radius, whereas in Lemur these two are divided by a sharp ridge. 

 In Lepilemur, however, this ridge is less pronounced. The olecranon closely resembles that of Lemur 

 varius but its medial apex is more produced inward; as seen from the proximal end the olecranon is less 

 rounded than it is in Lemur. The styloid process and the rest of the distal end recall this region in Lepi- 

 lemur. ' 



The ulna of Propithecus is especially close in all parts to that of Nntharctus, the principal difference 

 being the flattening of the flexor border in Propithecus, which contrasts with the sharp edge in Notharctus. 

 The olecranon of Propithecus is also rounder and more truncate and the sigmoid notch is wider. 



The ulna of Cebus is elongate and straighter, its olecranon massive and truncate, the coronoid process 

 higher, and the back of the shaft behind the sigmoid notch wide, with sharply projecting edges. The 

 interosseous border is not so sharp; there is no sharply rimmed fossa for the pronator (luadratus. The 

 styloid process is larger and more ball-like. 



In Alouatfa the ulna is remarkable both for length and stoutness; the shaft is roundly oval in section, 

 the olecranon wide and truncate, the styloid process very ball-like. 



The ulna of the marmosets is allied to the cebid type and has an expanded truncate olecranon. 



Manus 



Plate XXIX; Text Figs. 11, 83 



The description of the manus of Notharctus may be preceded with advantage by a description of 

 the manus of Lemur and of Cebus. 



The manus of Lemur is strongly prehensile, especially in the following characters: in the dried skele- 



