GLIRES OF THE SANTA CRUZ BEDS. 



419 



MEASUREMENTS. 



Lower dentition, length pj-my 025 



" " " m-r-mj- .018 



Lower incisor, width 006 



Lower incisor, thickness 0063 



Mandible, depth below my 017 



STEIROMYS DUPLICATUS Ameghino. 



(Plate LXVI, Figs. 1-2", 4, 5, 8, 9.) 



Steiromys duplicatus Amegh. ; Enumeration sistem., etc. ; 1887, p. 10. 



This is a large rodent, much exceeding Rrethizon dorsatum in size 

 Whether the manus and pes (PI. LXVI, figs. 8, 9), are properly referable 

 to this species, is not certain, because no teeth were found associated with 

 them, but they very probably are so referable, because, large as they 

 appear, they are but little larger, in proportion to the size of the skull, 

 than in the recent species. The incisors are larger and heavier than in 

 the latter, but the grinding teeth are relatively smaller and the diastema 

 actually shorter ; the raised external border of the lower incisor is distinct, 

 but there is no enamel ridge along the mesial border. A series of com- 

 parative measurements shows many differences of proportion from the 

 Canada porcupine, which is therefore included in the tables. In the first 

 table the individuals marked A. i and A.2 are in the Ameghino collection. 



MEASUREMENTS. 



