GLIRES OF THE SANTA CRUZ BEDS. 427 



MEASUREMENTS. 



Upper dentition, length 022 Ulna, width at sigmoid notch 0025 



" " " pfm-g 008 Femur, estimated length 036 



Upper incisor, width ooi " proximal width 0075 



" " thickness 0027 " distal width 006 



Lower dentition, length 017 Tibia, length 038 



" " " Pj-mj 008 " distal width 003 



Lower incisor, width 0012 " " thickness 003 



" " thickness 002 Calcaneum, estimated length 009 



Rostrum, length 013 Astragalus, length 0055 



" width at base on " width of trochlea 003 



" " " anterior end 006 Metatarsal III, length 015 



" dorso-ventral height oio " " proximal width 002 



Humerus, width of distal end 006 " " distal width 002 



" " "trochlea 0035 



SCIAMYS ROSTRATUS sp. nov. 



(Plate LXVII, Figs, 6-6".} 



This species is intermediate in character between S. principalis and S. 

 varians. The upper incisors have slightly convex and faintly grooved 

 faces and are somewhat broader than in S. varians. The rostrum is more 

 slender than in S. varians, less so than in S. principalis. Compared 

 with those of the latter, the nasals are less convex and narrow more pos- 

 teriorly, giving a broader dorsal surface to the ascending rami of the pre- 

 maxillaries. The frontals have no postorbital processes. The type is 

 No. 15,257 of the Princeton collection. 



MEASUREMENTS. 

 Upper dentition, length 0225 Rostrum, length 012 



" " " pA-m-3. 008 " width at base OIO 



Upper incisor, width 0015 " " " anterior end 0065 



" " thickness 003 " dorso-ventral height 008 5 



SCIAMYS TENUISSIMUS Ameghino. 

 Sciamys tenuissimus Amegh.; fenum. Synopt. des Mamm. Foss. de Pata- 



gonie, 1894, p. 68. 



This is much the smallest known representative of the genus and may 

 be" easily distinguished by its minute size. So far, it is known only from 

 mandibles, which differ from those of the larger species in the more pos- 

 terior position of the ascending ramus, leaving all the grinding teeth ex- 

 posed in side view ; so much of the masseteric fossa as is preserved, indi- 

 cates that it was relatively small. 



