EDENTATA OF THE SANTA CRUZ BEDS. 57 



Though nearly as long as the femur, exclusive of the great trochanter, the 

 tibia (Plate XV, fig. 4) is shorter than in Stegotherium; the proximal end 

 is broad and heavy, the facets for the femur well separated and without a 

 spine. The cnemial crest is extremely long and prominent, extending 

 down more than three fourths of the length of the shaft and with anterior 

 border curved outward, making the external side unusually concave. The 

 shaft is much compressed laterally, very thick antero-posteriorly, except 

 at the distal end, where these proportions are reversed. An interosseous 

 crest runs down the outer side of the shaft, for most of its length a mere 

 linea aspera, but becoming very prominent near the distal end. A cor- 

 responding crest appears upon the inner side of the fibula and at the distal 

 end the united crests are notched to form a subcircular opening, so that 

 in this region the coossification of the two bones is much less extended 

 proximo-distally than in Stegotherium. The astragalar facets are moder- 

 ately concave and are separated by a low intercondylar ridge ; the internal 

 malleolus is almost obsolete, but a stout and prominent tongue arises from 

 the plantar end of the intercondylar ridge, and internal to this is a shallow 

 tendinal sulcus. 



The fibula (Plate XV, fig. 4) is of very irregular shape and has a 

 sigmoid curvature ; the shaft is very narrow transversely, much extended 

 antero-posteriorly, especially at the proximal end, and diminishing dis- 

 tally ; the proximal portion of the shaft is deeply concave on the inner side ; 

 below this arises the interosseous crest already described. On the outer 

 side is a prominent ridge, which ends distally in an overhanging hook, 

 separated from the external malleolus by a sulcus. The distal end is 

 broad and thick, forming a stout malleolus; distally this process has a 

 facet for a shelf-like projection from the outer side of the astragalus and, 

 posterior to this, another and smaller facet for the calcaneum. 



In some other species of the genus the pes is very completely preserved, 

 but for P. robiistus the material available consists of only a calcaneum and 

 an astragalus. Since the differences are almost altogether in size, the 

 description of the hind-foot will be given in connection with the next 

 species. 



Restoration (Plate XI).- -The skeleton has a very massive appearance, 

 almost equalling that of Priodontes. Despite its elongate, tubular rostrum, 

 the head is very heavy, the neck short and thick and the trunk likewise 

 short and massive and characterized by the hump at the shoulders, the un- 



