356 University of California Publications in Geology [Vol. 7 



Although the caleaneum is of smaller size, the neck has a 

 relatively greater width than in M. jejfersonii. The superior 

 border of the fanlike tuber calcis is strongly concave, while the 

 inferior border is less arched than in the latter species. The 

 middle region of the inferior border is sharply edged. A depres- 

 sion occurs on the superior border close to the large astragalar 

 facet. Viewed from the proximal end (fig. 16), the postero- 

 inferior extremity is not decidedly directed toward either the 

 outer or the inner side, differing in this respect from both M. 

 jejfersonii and M. sierrensis. The lower half of the posterior 

 border is much thicker than the upper half. 



The proximal end is, on the whole, similar to that of M. 

 jejfersonii and has the following characteristics: The grooves 

 separating the three articular facets are well defined and are 

 broadest between the cuboidal and large astragalar facets. 

 Externally the large astragalar facet is flat, becoming slightly 

 concave internally as it curves down to the inferior border. The 

 small astragalar facet is concave in its longest (transverse) 

 diameter. The cuboidal facet is concave vertically and curves 

 toward the external margin. The inner lip is flattened almost 

 at right angles to the rest of the surface and articulates with 

 the astragalus. 



The facet for articulation of the cuneiform with the third 

 rigid metatarsal, no. 20001. is tri-lobed. The ventral lobe is 

 much the largest. Leidy states 15 that in M. jejfersonii this sur- 

 face is quadrate. Of the two dorsal lobes, the lateral is larger 

 than the medial one. The proximal face is concave both dorso- 

 ventrally and transversely. The articular facet for the second 

 metatarsal has its greatest diameter dorso-ventrally, while the 

 articular facet for the fourth metatarsal is widest transversely. 



The median distal convex surface of the metatarsal is oblique, 

 the lower end being nearest the inner side. At its ventral third 

 it curves slightly outward. The broad offsets on each side follow 

 this course more or less. The median convexity is wide and well 

 rounded in its dorsal two-thirds but narrows in its ventral third, 

 the arch becoming pointed. 



1S Leidv, J., Remarks on the Structure of the Feet of Megalonyx, 

 Trans. Anier. Philos. Soc, n.s. vol. 11, p. 107, pi. 6, fig. 1, 1860. 



