78 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I49 



as in Meniscotherium but is comparatively straight and not nearly so 

 slender. The Tetraclaenodon first metatarsal, however, is relatively 

 longer, being nearly two-thirds the length of the second, and only a 

 little more slender. The shaft is somewhat bowed as in Menisco- 

 therium. The base or proximal extremity, it is further noted, exhib- 

 its a short ventrolateral spur, unlike Meniscotherium, and the artic- 

 ular surface for the internal cuneiform is only slightly convex. 



Metatarsal II. — The second metatarsal of Meniscotherium is inter- 

 mediate in length between the third and fourth, but its distal extremity 

 is about even with that of the fourth in the articulated foot, because 

 of the more proximal position of the base of the second metatarsal. 

 The proximal surface for the middle cuneiform is nearly triangular in 

 outline, dorsoventrally elongate and slightly convex. Transversely 

 the facet is distinctly concave. The medial surface of the base is 

 somewhat roughened and a short distance distally exhibits a low 

 knob. Apparently, however, there is no faceting for either the inter- 

 nal cuneiform or the first metatarsal. The lateral surface of the 

 base, however, shows a slightly concave facet proximodorsally and 

 a smaller flattened facet proximoventrally for the external cuneiform. 

 More distally, the lateral surface conforms to the medial surface of 

 the third metatarsal base, but I find no evidence of articular contact. 

 The shaft maintains a width at least as great as the base, becoming 

 little wider distally, and is relatively compressed dorsoventrally. It 

 is essentially straight but may be slightly bowed dorsally in some 

 individuals. The convexity of the transversely wider distal extremity 

 is slightly oblique and shows a pronounced median keel only on the 

 ventral surface. 



Except for its more flattened proximal extremity for articulation 

 with the middle cuneiform and relatively wider distal extremity, the 

 second metatarsal in Phcnacodus appears very much like that in 

 Meniscotherium. That in Tetraclaenodon is more elongate and 

 relatively slender. The proximal surface of the base, like that in 

 Phcnacodus, is flattened although the outline is similar to that in 

 Meniscotherium. The distal extremity is broad in comparison with 

 the width of the base, but these are small relative to the length of the 

 shaft. 



Metatarsal III. — The Meniscotherium third metatarsal averages 

 about 5 or 6 percent longer than the second. The shaft is broad and 

 flat, increasing somewhat in width distally. The proximal extremity 

 shows the asymmetric T-shaped base so frequently encountered in 

 the mammalian third metatarsals. This surface for the external cunei- 



