Family MURIDAE. 



The family Muridce will be taken in its current acceptation, as far as 

 North American representatives are concerned, but with exclusion of the 

 genus Zapus* (Meriones or Jaculus of American authors), which, as type of a 

 separate family Zapodidce, will be treated in a subsequent memoir of this 

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

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



With the exclusion, then, of Zapus, the family Muridce is represented in 

 North America by only two subfamilies, Murince and Arvicolmce, 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 Muridce proper, which would then be constituted 

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

 family Muridce would render it rather equivalent to the subfamily Murince 

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

 brought under Muridce, 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 Murince 

 and Arvicolincv, the family Muridce may be recognized by the following 



characters : 



T 1-1 n 0-0 p 0-0 M 3-3 8 itt . ,, 

 L 1=1 ; C - =0 ; R 0=0 ; M - 3=3 = 8 = 1G tCeth - 



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

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

 mandible well developed and distinct. Tibia and fibula united below. 



* Zapus, «. g., Coues, Bullutiu U. S. Geol. Surv. Terr. 2d scr. No. 5, 1875, p. 253 



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