-k, . ; </>. ' 





Family MURIDAE. 



The family Muridte will be taken in itH current acceptation, as far oa 

 Korth American representatives are cnncern««l, but with exclusion of the 

 genus Zapua* {Meriones or Jaculua of American authors), which, as type of a 

 oeparate family Zapodlda, will be treated in a subsequent memoir of this 

 series. This genus differs sufficiently from any of the Murida in certain cranial 

 and dental characters, proportions of limbs, ana other features. 



With the exclusion, then, of Zapus, the fairtily Murida is represented in 

 North America l)y only two subfamilies, Murinas and Arvicolina, out of the 

 number of groups into which it is usually divided. We are inclined to believe 

 that the same considerations which induce us to eliminate Zapus as the type 

 of a distinct family (as has already been done by Gill), would require 

 certain Old World genera, in which the molars are more or less than §, to 

 be likewise separated from Murida proper, which would then be constituted 

 solely by forms in which there are § molars. Such construction of a 

 family Murida would render it rather equivalent to the subfamily Murine 

 of authors. But in our present ignorance of many exotic forms usually 

 brought under Murida, we do not venture upon general considerations touch- 

 ing the definition of the family at large. 



As represented in North America, and by the two subfamilies Murinee 



and ArvicoHna;, the family Mu ' '^ may be recognized by the following 



characters : 



T 1-1 r. 0-0 T> 0-0 ,, 3-3 8 .„, ,, 



^- r-1' ^- (Po' P- oiU' *^-3::3 = 8 = ^^*'^^**'- 



Anteorbital foramen a large pyriform slit, bounded exteriorly by a broad 

 plate of the maxillary. Coronuid, condylar, and descending processes of the 

 mandible well developed and distinct. Tibia and 6bula united below. 



* ZapuM, H. g., Codes, Ballotla U. S. Qeol. Surv. Terr. Sd ser. No. 5, 1875, p. 863 



