798 



RODENTIA 



from a bright russety wood-brown nearly to buff and greyish 

 drab ; underparts whitish, sometimes a nearly pure bluish or 

 creamy white, more often tinged with slaty or washed with 

 yellowish brown, the line of demarcation along sides always 

 sharply defined in adults ; a yellowish brown spot or longitudinal 

 streak usually present on middle of chest between fore legs, this 

 spot rarely spreading to form a complete collar ; teeth rather 

 weak, the alveolar width of m^ less than half width of palate 

 between tooth-rows ; m'^ with three distinct tubercles on outer 

 side, but neither this tooth nor m^ with well-developed 

 supplemental loop behind third outer tubercle (sometimes a 

 slight trace of this loop in m^) ; outer side of m^ and m^ with 

 noticeable cingulum-like ledge extending nearly entire length of 

 crown and bearing distinct though minute cusps ; skull remaining 

 light and smooth even in extreme old age, the interorbital 

 margins not beaded, the brain-case never developing evident 

 lateral ridges ; rostrum not specially elongated ; mandible with 

 well developed coronoid process. 



External characters. — External form slender, much as in the 

 house mouse, but feet, eyes and ears i-elatively larger. Ear 

 extending slightly but evidently beyond eye when laid forward, 

 its general outline broadly ovate, sometimes a little flattened 

 above and on posterior border ; antitragus reduced to a low 

 inconspicuous ridge not capable of closing meatus ; surface of ear 

 finely pubescent. Muzzle with ill-defined naked area surrounding 

 nostrils ; nostril opening obliquely forward and outward, wider 

 anteriorly than posteriorly, its inner and lower margin thickened 

 and irregularly wrinkled ; a deep furrow under lower border and 

 another dividing nostrils in median line and continuous below 

 with cleft in upper lip. Feet slender, without special modifica- 

 tions. Thumb reduced to a mere tubercle, the upper surface of 

 which is covered by the rudimentary nail ; palm naked, 

 5-tuberculate, the tubercles well developed, distinct, the two 

 hindermost slightly larger than the others, but showing no 

 tendency to unite along median line, the surface of the palm 

 between the tubercles irregularly wrinkled ; under surface of 

 digits with five or six deep transverse furrows. Hind foot 

 relatively longer and more slender than in the house mouse, the 

 three median toes sub-equal, the outer extending almost to end of 

 first phalanx of fourth, the inner scarcely to base of first phalanx 

 of second, the under surface marked off by conspicuous cross 

 furrows into well defined, entire, scales or plates, of which there 

 are seven or eight on the longer toes. Sole naked except at 

 sides of heel (this hairy area sometimes extending completely 

 adross), its surface papillose in region among tubercles, rugose at 

 heel, smooth between last tubercle and wrinkled posterior 

 portion ; tubercles six, well developed and distinct, ovate in 

 outline, the four anterior largest and sub-equal, the postero- 

 external smallest. Tail about as long as head and body. 



