74 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I49 



at the ventromedial angle of the proximal surface. The lateral sur- 

 face of the navicular shows a dorsoventrally elongate and slightly 

 convex facet along its more proximal portion for articulation with 

 the cuboid. On the ventral surface of the navicular, lateral to the 

 notch, is a small knob or process that may have supported a part 

 of the insertion for the tibialis posterior. It is located just above 

 the posterior extremity of the facet for the external cuneiform but in 

 Meniscotherium evidently does not make contact with that bone. 



A few differences were noted with respect to the Phenacodus 

 navicular, although the two are rather similar. On the proximal rim 

 the ventrolateral prominence is more significant than that of the 

 ventromedial angle, and projects laterally as well as proximally in 

 Phenacodus. The more obliquely facing facet for the cuboid is proxi- 

 modistally deeper and rides well up on the proximoventral promi- 

 nence. Also, the ventral tubercle is larger, more median in position, 

 and its distal surface carries a small facet, not seen in Meniscotherium, 

 for articulation with the ventral extension of the external cuneiform. 

 The facet for the middle cuneiform appears relatively longer and less 

 convex. 



In the Tetraclaenodon navicular the ventral tubercle and the ventro- 

 lateral prominence of the proximal rim together form a strongly 

 developed, oblique, and ventrolaterally projecting process. This 

 results also in a dorsoventrally concave surface articulating with the 

 cuboid. 



Cuboid. — The Meniscotherium cuboid viewed dorsally in an artic- 

 ulated foot appears relatively short proximodistally, with the exposed 

 area in the form of a parallelogram or nearly rectangular, inasmuch 

 as the articular surface for the calcaneum extends distally well down 

 the dorsal surface. Disarticulated, the calcaneal facet is seen to be 

 dorsoventrally very convex and highly oblique in a nearly transverse 

 plane. Moreover, the dorsal and ventral surfaces are convergent in 

 a proximolateral direction. Distally the ventral surface shows a 

 pronounced ventromedial flare, ventrally covering the deeply im- 

 pressed peroneal groove. The distal surface anterior to the elongate 

 peroneal groove is nearly oval in shape and essentially concave both 

 dorsoventrally and transversely. The surface is principally for artic- 

 ulation with the fourth metatarsal, although the lateral extremity of 

 the transversely elongate oval flattens out or is somewhat deflected 

 proximally for articulation with the fifth metatarsal. Also, the ven- 

 tral margin of the oval facet is rounded into the peroneal groove for 

 the recurved surface of the fourth metatarsal. The proximal portion 



