4 Miller — A Jumping Mouse {Zapus insignis), 



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

 darker shade. Z. iii-^iigai.^ 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 insignis, 

 Avhile, in hudsonius the black hairs are the more numerous on 

 the head and face. The gray muzzle is much paler in insignis 

 than in hudsonius. Tlie 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. insignis the ears are lined with yellow 

 and clothed outside with dusky and yellow hairs in about equal 

 in-o])ortions, the latter forming a pale though never white 

 edging. 



Two young examples of Z. hudsonivs (S juv. No. HI 2 '^^^'^ 

 $ juv. No. nil, 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 occasionalh' have 

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

 Sitomys aniericanus; also occasionally in Mus musculus, Arvicola 

 riparius, and Blarina hrericauda. It is thus especially notewor- 

 thy that in Zapus insignis this character, elsewhere merely acci- 

 dental, should liaA^e 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, Avith 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 u[)per mohir appears in some sj^ecimens 

 slightly longer proportionally. 



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

 the alisence of the premolar might be due to the age of the speci- 

 mens at hand and consequent sliedding of tlie tooth. That this 

 view is incorrect is conclusively sliown by the material now 

 availal)lo. Specimens of Z. hudsonius with teeth excessivel}^ 

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

 found a trace of this tooth, even in individuals so 3'oung that 

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



