Peterson: The Osteology of Promerycochcerus. 213 



A characteristic feature of the astragalus in the type is the very 

 shallow pit^^ on the internal face of the trochlea, partly occupied by 

 the free end of the internal malleolus of the tibia, which in most 

 Merycoidodonts is rather well-developed. In P. Qarrikeri this pit is 

 especially well-developed in order to accommodate the extra large 

 internal malleolus. This is a condition which helps to strengthen 

 the ankle in the earlier species, while in the present form the malleolus, 

 as stated in the description of this bone, is not so large, the free end 

 is not directed as strongly outwardly, and the interlocking feature is 



40 41 



Fig. 40. Dorsal view of pes of Promerycochcerus vanlasselensis. 



No. 1230; \ nat. size. 



Fig. 41. Plantar view of pes of Promerycochcerus vanlasselensis. No. 1230; 



i nat. size, cal, calcaneum; a, astragalus; n, navicular; c, cuboid; ec, ento- 



cuneiform; x, metatarsal I, or a lodged sesamoid; II, III, IV, V, second, third, 



fourth, and fifth metatarsals respectively. 



consequently much less noticeable. The external condyle of the 

 proximal trochlea is, as usual, very much higher and stronger than the 

 internal. The latter is less rounded on its edge than in P. carrikeri 

 and is more like that of Merycoidodon culhertsoni. The distal trochlea 

 is rather shallow and the navicular facet is somewhat broader than 

 in P. carrikeri. The astragalus as a whole is comparatively low and 

 broad, but not to the same extent as in Merycochcertis from later 

 horizons. 



21 In another individual, which has been referred to this species, there is an 

 unusually deep and rounded tendinal pit below the malleolar articulation, which is 

 scarcely represented in the type. 



