GLIRES OF THE SANTA CRUZ BEDS. 



429 



heavier, and the inferior margin of the angle is unusually broad, owing to 

 the development of the masseteric and pterygoid crests. 



The parts of the skeleton have already been described in the account 

 of the genus. The tibia, which seems to have been of nearly the same 

 length as in S. varians, has a somewhat heavier distal end, while the me- 

 dian metatarsal is notably shorter than in that species. 



MEASUREMENTS. 



Upper dentition, length 023 



" " " pA-mi 0075 



Upper incisor, width 002 



" " thickness 003 



Skull, interorbital width 045 



Rostrum, length 012 



" width at base oil 



width at anterior end 0085 



" dorso-ventral height 0085 



Lower dentition, length 020 



" p T -m 3 008 



Lower incisor, width 002 



" " thickness 003 



Diastema, length 008 



Mandible, depth below p ? 007 



Metacarpal II, length 007 



" proximal width 0015 



" distal width 0017 



Metacarpal III, length 075 



" " proximal width 002 



" " distal width 002 



Metacarpal IV, length 0065 



Digit IV, length 0165 



Digit IV, phalanx i, length 004 



a tt tt o ** OO2 



" " " 3, " 005 



Tibia, distal width 003 5 



" " thickness 003 



Calcaneum, length 009 



Astragalus, length 0055 



" width of trochlea 003 



Metatarsal I, length 0065 



" " proximal width 0013 



" " distal width ooi 3 



Metatarsal II, length 013 



" " proximal width 0015 



" " distal width 002 



Metatarsal III, length 0125 



" " proximal width 002 



" " distal width 002 



Metatarsal IV, length 012 



" " proximal width 0015 



" " distal width 002 



Metatarsal V, length oio 



" " proximal width 0025 



" " distal width . .002 



SCIAMYS ROBUSTUS Ameghino. 

 Sciamys robtistus Amegh. ; Enum. Synopt. des Mamm. Foss. de Pata- 



gonie, 1894, p. 68. 



This incompletely known species differs from the others in such a way 

 as to suggest that better material may require its generic separation. In 

 the Princeton collection it is represented only by one specimen (No. 

 15,824) consisting of the symphysial region of a mandible, with both in- 

 cisors in place, and retaining the alveolus of p T , together with some frag- 

 ments of limb bones. S, robustus is the largest known species of the 

 genus, and the incisors are of somewhat uncommon proportions, the thick- 



