GLIRES OF THE SANTA CRUZ BEDS. 469 



condyles are widely separated by the broad sulcus for the crucial liga- 

 ment, and the hook-like process from the postero-external angle of the 

 outer condyle is smaller than in the recent genus. The distal end has an 

 asymmetrical surface for the astragalus, with much larger external con- 

 dyle, prominent intercondylar ridge, which is invaded by a sulcus from 

 the dorsal side, and very large posterior tongue ; the internal malleolus is 

 small, but distinct. 



The fibula is very much less reduced than in Dolichotis and is even 

 relatively stouter than in Cavia; the proximal end is narrow, but thick 

 antero-posteriorly, the shaft is very irregular and the distal end forms a 

 heavy external malleolus, grooved by the sulcus for the peroneal tendon 

 on the outer side. 



The pes (Plate LXIX, fig. 10) though far larger than the manus, does 

 not exceed it so much as in Dolichotis and has more the proportions seen 

 in Cavia; in structure it resembles that of the former genus, with several 

 minor differences, the tarsus resembling that of Cavia. The calcaneum 

 has a short heavy tuber, of trihedral shape, broad on the plantar side and 

 contracting to a blunt edge on the dorsal ; the external astragalar facet is 

 large, convex and very oblique, presenting inward ; the sustentaculum is 

 heavy and not very prominent, with small, subcircular facet ; the cuboid 

 facet is deeply concave and very oblique, presenting inward rather than 

 distally. The astragalus differs considerably from that of Dolichotis, 

 especially in the narrowness of the neck and head and in the absence of 

 the deep pit distal to the trochlea which is seen in the modern genus ; the 

 trochlea is very asymmetrical, owing to the large size of the outer con- 

 dyle, and is quite deeply grooved. The navicular also is much narrower 

 than in the last-named genus and the cuboid far shorter proximo-distally, 

 and thicker planto-dorsally, but has a similar massive process from the 

 whole plantar side, to the distal end of which is attached a sesamoid bone, 

 just as in the modern genus ; the facet on the distal end for metatarsal V 

 is minute. The meso- and ectocuneiforms, especially the latter, are 

 smaller than in DolicJiotis ; the entocuneiform has not been found, but its 

 presence is demonstrated by the facets upon the second metatarsal. 



It is almost certain that the number of functional metatarsals is three; 

 these are very much larger than the metacarpals. Metatarsal II is long, 

 relatively slender and asymmetrical ; owing to the small size of the meso- 

 cuneiform, its proximal end rises much above that of III, as is universal in 



