4 Miller A Jnmpiny Mouse (fripu* insignis), 



belly is apt to be more strongly defined and of a somewhat 

 darker shade. Z. in*iynix is always pure white beneath, never 

 showing a trace of the buffy suffusion commonly seen in Z. 

 hudsonius. Yellow is the prevailing color on the head of insign /*, 

 while in hudsonius the black hairs are the more numerous on 

 the head and face. The gray muzzle is much paler in ins'iyni* 

 than in hudsonius. The ears of the two species differ notably in 

 color as well as in size, those of Z. hudsonius being more thickly 

 haired and blackish throughout, except for a sprinkling of yel- 

 lowish hairs on the outside and a narrow, pale sometimes 

 white border, while in Z. inxlyni* the ears are lined with yellow 

 and clothed outside with dusky and yellow hairs in about equal 

 proportions, the latter forming a pale though never white 

 edging. 



Two young examples of Z. hudsonius ($ juv. No. 1432 and 

 $ juv. No. 1433, Peterboro, N. Y., August 1, 1892), otherwise per- 

 fectly typical, have 8 mm. of the distal end of the tail white. 

 These are the only specimens of the species in which I have 

 seen the slightest indication of this character, but it is to be 

 expected since most of our small mammals occasionally have 

 white-tipped tails. I have repeatedly noticed it in two races of 

 Sitomys americanus ; also occasionally in MH* nmxctdus, Arvicola 

 ripariuSj and Blarina brecicauda. It is thus especially notewor- 

 thy that in Zap as insignis this character, elsewhere merely acci- 

 dental, should have become so fixed as to be practically diag- 

 nostic. 



The skull of Zapus insignis closely resembles that of Z. hud- 

 sonius, but is throughout slightly broader and heavier, with a 

 less highly arched brain case. Except for its somewhat larger 

 size, the mandible shows no points of difference. 



The teeth are all somewhat heavier than in Z. hudsonius and 

 the crown of the middle upper molar appears in some specimens 

 slightly longer proportionally. 



In the original description of Z. insignis it was suggested that 

 the absence of the premolar might be clue to the age of the speci- 

 mens at hand and consequent shedding of the tooth. That ( liis 

 view is incorrect is conclusively shown by the material now 

 available. Specimens of Z. tui<ls<nuu$ with teeth excessively 

 worn still retain the premolar, while in Z. inxignis I have never 

 found a trace of this tooth, even in individuals so young that 

 the posterior molar has not cut through the gums. I have seen 



