Famiry MURIDAE. 
The family Muride 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 Zapodide, will be treated in a subsequent memoir of this 
series. This genus differs sufficiently from any of the M/uride@ in certain cranial 
and dental characters, proportions of limbs, and other features. 
With the exclusion, then, of Zapus, the family Muride is represented in 
North America by only two subfamilies, Murine and Arvicoline, 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 3, to 
be likewise separated from Muride proper, which would then be constituted 
solely by forms in which there are 3 molars. Such construction of a 
family Muride 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 Murine 
and Arvicoline, the family Muride may be recognized by the following 
characters : 
| 0-0. 4, 8-8 8 
* 0-0’ CO 323s 
— 16 teeth. 
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, n. g., COUES, Bulletin U. S. Geol. Sury. Terr. 2d ser. No. 5, 1875, p. 253 
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