6 MONOGRAPHS OF NORTH AMERICAN RODENTIA. 
Diagnostic table of some cranial and dental characters of North American Murtp2—Continued. 
MURID&. 
MURINE. ARVICOLINE. 
; Mures. Sigmodontes. 
Fener: Arvicola. 
.| a 7 s AMS P 
BISiSlelelsielz Ble) 2/518]. 
o |S/elelalslelelSielelz|elelalz 
SB |S|SlS/S/PIEIEISISIS/EI RIS 5/2 
BS |FZIDISIPISIS6/ ASIN IAlAla|alO|m 
Molar crowns: 
Tuberculate, crenate-edged : 
Tubercles triseriatim. ..-.---..---------- + By Wace eet | poeel esate lead aed! os tos Wc fcalos If ce. 
Tubercles biseriatim .-......--.---------| ------ +/+})+]+]+]/+ 
Prismatic : | 
Sharply angular, both sides -.-...--..---| ------ i l55 | (eo) oa fee eallfaeiarllar\iar|)sryfice || oo ilar] o> 
Sharp one side, obtuse the other.--...---| .---.- P| | ee Ree toa Pos fecal | Woe | foo! [fac | isa iste 15 
When fully worn, consisting essentially of one 
dentine area, within an enamel wall, which, 
however deeply plicate, does not fuse from 
opposite sides.........--...--------------+---- + +/+/4+]/4+/4+)/4+ 
Even after wear still consisting of several den- 
tine islands, owing to fusion of the enamel 
walls from opposite sides.......----.----------| ------ wef ee] ee] ee] --] ee Pt] 4] 4] 4) 4+]-+#] +) +/+ 
Molar series: 
Strongly convergent anteriorly...-.-..----------| «----- Sel ee hse || soil fee aati fse Pool se)! so |pa> | Sei Se Ise 
Little, if any, convergent anteriorly -.-..-.. Bi icosaes Bo ilPast|lcta | ae Wiss =I +/+})+)/+)4+]--]--]-- 
Rather divergent anteriorly. .....-.--------.---- fe |e) || ae |) | |) 
Upper molars : | 
Of approximately equal size throughout.-.-..---) ------ J--|--|--}--]--]--]+] 4] 4) 4] 4]4+]4] 414+ 
Decreasing in size from before backward. ....--. ++ |+)+]+ [+) + 45) 
| 
SUBFAMILY MURIN A. 
The characters of this subfamily having already been given in sufficient 
detail for present purposes, we may at once proceed to consider its subdivision 
into the two tribes or series of genera; namely, Mures and Sigmodontes. This 
separation of the Old World (Aures) and New World (Sigmodontes) repre- 
sentatives of the subfamily seems to us warranted, and not alone upon geo- 
graphical grounds; for a decided difference in dentition is found, serving for 
their immediate identification. 
Mures.—Molars of upper jaw, with the tubercles in three series. Palate 
extending back of the molars. (Paleeogzean.) 
SremoponTEs.—Molars of upper jaw, with the tubercles in two series. 
Palate ending opposite last molars. (Neog:ean.) 
The Mures which occur in North America,—namely, four species 
