MURID^E— ARVICOLIN^— PEDOMYS. 



209 



Notb. — Nos. 8370-71, apparently of this species, are too young for positive identification. The teeth are scarcely cut; 

 but, so far as wo can judge, the back upper molar will havo but one external closed triangle, and a posterior Y-shaped treffle. 

 The meatus seems to be surrounded by a faint rim, but the upper margin of the ear is not inflected, the concha being per- 

 fectly flat. 



Subgenus PEDOMYS, Baird. 



Arvieola sp., Atjctorum. 



= Pedomys, Baird, M. N. A. 1857, 517 (type, Arvieola austerus LeC). — Coues, Proc. Acad. Nat. Sci. 

 Phila. 1874, 190. 



Chars. — Posterd-superior molar with an anterior transverse loop, two 

 interior triangles, one exterior triangle, and a posterior U-, V-, or Y-shaped 

 loop (as in Pitymys and Chilotus). Medio-superior molar with an anterior, 

 two exterior, and only one interior triangle (lacking the supplementary postero- 

 interior spur or triangle of Myonomes). Anteroinferior molar with a posterior 

 transverse loop, two interior closed triangles, one exterior closed triangle, 

 another exterior and another interior open triangle, and an anterior irregular 

 trefoil. Other molars as in Arvieola at large. Ears concealed, without 

 inflected margin of conch or rim in front of meatus ; antitragus highly val- 

 vular, as usual. Tail in the type of the subgenus about equal to the head 

 (about one-third the head and body), in other species not more than one- 

 fourth the trunk, and thus as short as in Pitymys. Perfect plantar tubercles 

 only five. No special cranial characters, and external form as in Myonomes 

 (except shorter tail), or much as in Arvieola at large. Pelage grizzly and 

 rather "austere"; the under parts usually with a peculiar muddy tinge. 



Under head of Arvieola we have already diagnosticated this section, and 

 after the further remarks just made there is little to say. There are no tan- 

 gible cranial characters ; and, as to the external characters, they are with diffi- 

 culty describable as any different from those of Myonomes ; but the tail is 

 shorter, and the animals appear to be even more squat and bunchy than M. 

 riparius. There are only five perfect plantar tubercles, though the rudiment 



14 M 



