94 GREGORY: NOniARCrUS, AN AMERICAN EOCENE PRIMATE 



Comparative Measurements of the Tibia 





A'', osborfii 

 No. 11474 



A''. tenehrosu» 

 No. 1727 



L. mongoz 

 No. 31254 



L. mo7igoz 

 No. 22886 



L. varius 

 No. 18040 



Cebu-s apicidatm 

 No. 30200 



Length of Tiliiii, distal to proximal 



facets 

 Tibio-femoral Ratio 



101 . 

 .82 



112. 

 .81 



110. 

 .82 



115. 

 .89 



134.6 

 .88 



131 . 

 .90 



The tibia of Propithecus is more elongate and slender than that of Nothardus, but is otherwise simi- 

 lar. The lower anterior tuberosity is less pronounced and is much nearer the upper end of the shaft. 

 (Plate XXVI.) 



The tibia of Cebus is longer and straighter than that of Notharctus, the proximal end is flatter with 

 a lower spine, the lower anterior tuberosity is much less proininent, the distal articular facet has deeper 

 concavities for the trochlea of the astragalus, the internal malleolus is more produced downward, the 

 distal end as seen from the rear is wider antl flatter at the lower edge. 



Fibula 

 Text Fig. 17 



The fibula of Notharctus is essentially similar to that of Levinr; as in i-ecent lemurs and indrisines 

 the external malleolus is produced outward more than downward, and the facet for the astragalus is 

 gently inclined to the vertical plane in correlation with the gentle inclination of the external facet of the 

 astragalus. The fibula differs from that of Lemur mongoz in its sharpty curved shaft and relatively more 

 robust and distal ends. 



In Propithecus the fibula is essentially the same as that of Notharctus, but more elongate and somewhat 

 less curved. (Plate XXVI.) 



Cebns and its allies have the fibula much more elongate and slender, with almost straight shaft. 

 The external malleolus is produced downward rather than outward, and extends down nearly to the 

 level of the internal malleolus. The facet for the astragalus is nearly vertical in correlation with the 

 sub vertical plane of the external facet of the astragalus. 



The fibula of the marmosets is essentially the same as that of Cebus; the distal end of the fibula is 

 closely appressed to and bound by the interosseous membrane to the tibia; occasionally the junction 

 with the tibia a centimeter up the shaft. The external malleolus is neai-ly level with the internal mal- 

 leolus, and the facet for the astragalus is vertical. 



Pes 



Plates XXX, XXXI; Text Fig. 84 



The pes of Notharctus is represented by a number of specimens, pertaining chiefly to osborni, 

 N. tyranmis and A^. tenebrosus, which afford knowledge of every element of the foot except certain of the 

 phalanges. The principal specimens are as follows: Xo. 11474 (part of the paratype skeleton of A^. 

 osborni) the greater portion of the right pes and portions of the left; No. 11466 (associated with type 

 skull of A^. osborni), left calcaneum, right entocuneiform; No. 11478 (part of skeleton referred to A^. 

 tyrannus), right pes lacking phalanges, except on hallux, left astragalus, calcanevmi, meso- and ectocunei- 



