GLIRES OF THE SANTA CRUZ BEDS. 43! 



contour of the facial region is straighter, the nasals are narrower behind, 

 broadening more anteriorly, where they are even less convex ; the post- 

 orbital process of the frontal projects more abruptly ; the incisive foramina 

 are larger and the posterior nares of a different shape. 



The specimens described as A. messor are apparently somewhat larger 

 and more robust individuals of the present species. 



MEASUREMENTS. 

 Upper dentition, length 0245 Rostrum, length 014 



" " " pA-m- 3 0075 " width at base 012 



Upper incisor, width 0025 " " " anterior end 009 



" " thickness 0032 " dorso-ventral height 0095 



Skull, interorbital width 0105 



ACAREMYS KARAIKENSIS Ameghino. 

 Acaremys karaikensis Amegh. ; Rev. Argent, de Hist. Nat.; T. I, 1891, 



p. 299. 



Though originally separated from A. murinus on account of its larger 

 size, the transitions in this respect are so complete, that the species cannot 

 be maintained for that reason alone. However, the validity of the species 

 is evident from the character of the incisors, which are narrower than in 

 the preceding species, and from the shape of the rostrum, which is broad 

 at the base and tapers forward rapidly. 



ACAREMYS MAJOR sp. HOV. 



, The type specimen (No. 15,366), a skull without mandible and con- 

 siderably distorted by pressure, was collected at Killik Aike by Mr. O. A. 

 Peterson. It is so much larger than any other known representative of 

 the genus that it probably represents a distinct species. Though the 

 skull markedly exceeds that of A. murinus in size, the incisors are actually 

 narrower, while the grinding teeth are notably larger, especially in width, 

 and are of different relative sizes, p A and m 1 being nearly equal, while 

 m- and a are considerably larger ; m 3 - is not at all reduced, as it is in A. 

 murinus. The rostrum is long, narrowing forward somewhat, but quite 



broad, even anteriorly. 



MEASUREMENTS. 



Upper dentition, length 030 Skull, interorbital width 017 



" " " pi-m 0085 Rostrum, length 020 



Upper incisor, width 002 " width at base 014 



" " thickness 003 " " " anterior end 0085 



Skull, length 057 " dorso-ventral height oio 



