GLIRES OF THE SANTA CRUZ BEDS. 407 



rostrum, the incisors are narrow and appear to be even more so than they 

 actually are, because of the strong convexity of their anterior faces. 



MEASUREMENTS. 



No. 9,512. No. 15,555. Amegh, Col. 

 Upper dentition, length ................ 029 .028 



" " " pA-mi .......... 013 .013 



" " " mi-mi ......... oio .010 



Upper incisor, width .................. 002 .002 



" " thickness ............... 0025 .0025 



Lower dentition, length .............. .022 



" pj-mj ........ .013 



" " " m T -ms ........ .0095 



STICHOMYS REGIUS Ameghino. 



(Plate LXV, Figs. 16, 20, 20.) 



Stichomys regius Amegh. ; Enum. Synopt. des Mamm. Foss. de Patagonie, 



1894, p. 70. 



This species is distinguished from the preceding one by its somewhat 

 larger size and more robust proportions and by the broader rostrum and 

 heavier incisors. So far as the available material goes, these differences 

 appear to be quite constant, though it is quite possible that more numerous 

 specimens might show them to be merely individual variations. The fol- 

 lowing measurements of the upper teeth are taken from a specimen in the 

 collection of the American Museum of Natural History (No. 9,495) and 

 those of the lower teeth from a mandible in the Princeton Museum (No. 



MEASUREMENTS. 



Upper dentition, length .............. 033 Upper incisor, thickness ............. 003 



" " " pA-mi ........ 0145 Lower dentition, length ............. 026 



" " " mi-mi ........ 01 1 " " " Pj-mj ....... 015 



Upper incisor, width ................ 0025 " " " m-j m^ ....... 0115 



STICHOMYS ARENARUS Ameghino. 

 Stichomys arenarns Amegh. ; Enum. Synopt. des Mamm. Foss. de Pata- 



gonie, 1894, p. 70. 



In this species, which is as yet known only from a single mandible, the 

 series of grinding teeth has the same length as in S. regularis, but the 

 horizontal ramus of the jaw is so much more slender as to give it quite a 

 different appearance from that of the typical species. 



