EDENTATA OF THE SANTA CRUZ BEDS. 79 



The dental formula is & and the anterior upper teeth, though of similar 

 form to those of P. exilis are distinctly larger ; the same is true of the 

 lower teeth, the crowns of which do not protrude so much above the 

 alveoli as in the preceding species. 



The skull is of very similar appearance to that of P. exilis and the dif- 

 ference in size is trifling, but there are some not unimportant differences 

 of proportions. The cranium is more vaulted and rises higher above the 

 occipital crest ; the constriction in front of the orbits is more gradual, and 

 the rostrum longer and more tapering. The basioccipital is rather more 

 distinctly keeled in the median ventral line and its posterior border is 

 much more deeply notched, giving to the narrower foramen magnum quite 

 a different shape. The mandible displays a number of characteristic dif- 

 ferences ; the horizontal ramus is stouter, straighter, with a less sinuous 

 ventral border, and ending anteriorly in a much blunter point ; the eden- 

 tulous part is a little shorter and much less decurved. In addition to the 

 two mental foramina seen in P. exilis, there is a third, which opens on 

 the ventral side of the ramus, on the same transverse line as the anterior 

 of the two lateral foramina. The ascending ramus is more erect, less 

 inclined backward than in the other species, the angular process shorter 

 and decidedly less elevated above the level of the horizontal ramus, and 

 the condyle larger. 



In the subjoined table the measurements are taken from No. 15,567. 



MEASUREMENTS. 



Upper dentition, length 023 Astragalus, width of distal end 0035 



Lower " " 027 Calcaneum, length 013 



Skull, length in median basal line 056 " " of tuber 009 



" greatest length 070 " width of distal end 004 



Cranium, length to anterior rim of orbit. .03 1 Metatarsal I, length 009 



Occiput, height 02 1 " " width of proximal end . . .0035 



" width at base 029 " " " of distal end 002 



Palate, length 036 Metatarsal II, length 015 



Rostrum, width of anterior end 007 " " width of proximal end . . .004 



Mandible, length 05 1 " " " of distal end 0035 



" of edentulous part 53 Metatarsal III, length 016 



depth below g 005 " " width of proximal end. . .004 



thickness below g- 004 " " " of distal end 004 



height of condyle 0185 Metatarsal IV, length 014 



Astragalus, length 008 " " width of proximal end. .003 



width of trochlea 006 " " " of distal end 0035 



