692 



MR. O. THOMAS ON A NEW 



[Dec. 14, 



in which they reach to the end of the first phalanx of the fourth 

 digit'. Tail about equal in length to the body without the head. 



Quality and coloration of the fur almost exactly as in pale 

 specimens of Sigmodon hispidus. Say and Ord, to which this species 

 bears a most remarkable resemblance. Fur of the back of two 

 kinds : the woolly underfur dark slaty blue ; and of the longer hairs 

 some are black for their whole length, and others have a long 

 yellowish-white tip. Belly white, with a slaty tinge at the roots of 

 the hairs ; sides of the muzzle yellowish ; whiskers brown. 



The anterior edge of the root of the zygoma is rather deeply 

 emarginate in front, though not so much so as in li. cuniculoides. 

 The palate agrees more with that of It. chinchilloides, ending just 

 behind the molars, and being less ridged and excavated than in 

 B. cuniculoides. Posterior nares not narrowed by the approxima- 

 tion of the pterygoids. Incisive foramina short, ending in front of 

 the first molar. Pterygoid fossae deep. Frontal bones with a 

 strong concavity just behind the orbital constriction, as shown in the 

 drawing (see fig. 2). 



Fig. 2. 



Skull of ReUhrodun alsioni. 



The teeth are very different from those of any of the other sj)ecies 

 of the genus, being much shorter and broader, so that the whole 

 length of the molar series is contained twice in the distance 

 between the incisors and the first upper molar, while in none of the 

 others is it contained more than once and a half; and the second 

 upper molar is distinctly broader than long, while in tiie other 

 species the opposite obtains. The molars of the type specimen are 

 too much worn down for their pattern to be described ; but the 

 woodcut (fig. 2) sliows their general shape. The upper incisors 

 have a deep and distinct groove down the centre of their front 

 surface, a groove much more strongly marked than in any of the 

 other species. 



' This ebarac'ter, wbich ^Yaterllouse appears to have overlooked, «eems to 

 carry out still further the parallelism between Sigmodon and Oryzomys on the 

 one band and the two '' subgenera " of Rfif/irodon on the other, whicb Dr. 

 Coues drew attention to when subdividing this genus (see infra, p. 694). 



