EDENTATA OF THE SANTA CRUZ BEDS. 2Oy 



The edentulous beak of the mandible is short and the chin rises quite 

 steeply, with a concave profile ; the ascending ramus has a less sinuous 

 ventral border than in H. longiceps, and the coronoid process, which is 

 rather low and narrow, is more recurved, making a deeper sigmoid notch ; 

 the angle is broad and heavy, but not very long, and has the ventral bor- 

 der inflected, which makes the external side convex and the inner side 

 concave. The postero-external opening of the dental canal is in the 

 ascending ramus and presents so directly forward as to be nearly invisible 



in side view. 



MEASUREMENTS. 



Lower dentition, length 036 f width 0073 



" " " j_f 025 Mandible, length from condyle 103 



j-, length (i. e., an tero-posterior diameter) .004 " " " angle 109 



" width (i. e., transverse diameter) 005 " " of predental beak . . . .025 



5-, length 0065 " depth below j : .024 



" width 009 " thickness below 3- 013 



3-, length 0065 " length condyle to y 045 



" width 009 " height of coronoid 047 



T , length 0075 " " " condyle 037 



Associated with this mandible are a calcaneum and astragalus, so pecu- 

 liar as to indicate the perfect distinctness of the species, provided, of 

 course, that the association is not accidental. The astragalus has the nar- 

 row and elongate shape common throughout the family, but the trochlea 

 has quite a different shape from that of the other species ; its distal por- 

 tion is relatively broader and the proximal part narrower, making the 

 tibial border more oblique ; the inner condyle is shorter proximo-distally, 

 more elevated and convex, and with a much more distinct tendency toward 

 the assumption of the odontoid form than in any other known species of 

 the genus, or, indeed, of the family. The calcaneum has the form com- 

 mon to all the members of this genus, but is distinguished by the close 

 approximation of the two astragalar facets, which are separated only by a 

 very narrow sulcus, and by a slight reflection of the inner facet upon the 

 dorsal side of the sustentaculum. 



MEASUREMENTS. 



Astragalus, length 030 Calcaneum, length 05 1 



Astragalus, width of trochlea, proximal " proximal width of tuber. .. .044 



end 016 " width of tuber at neck 015 



Astragalus, width of trochlea, distal end .02 1 " " " distal end 023 



" " neck . .016 



