REVISION OF THE JUMPING MICE OF THE GENUS ZAPUS. 7 



Very little is known of the geological history of Zapus, except that 

 the genus dates back to the Postpliocene. In 1871 Prof. E. D. Cope 

 recorded a inandibular rainus with incisor and second molar of a Jump- 

 ing Mouse from the Port Kennedy Bone Cave in Pennsylvania. 1 On 

 account of lack of recent specimens for direct comparison he was some- 

 what in doubt as to the specific identity of the remains, but referred 

 them to Jacultis (= Zapus) Inidsonius? 



External characters. The external and cranial characters of Zapus 

 have been so exhaustively treated by Baird, Cones, and others that 

 a brief reference to them here will be sufficient. The body is consider- 

 ably enlarged posteriorly, the hind legs and tail greatly developed, the 

 forelegs rather short, and the ears somewhat longer than the surround- 

 ing fur. All the species agree closely in color and markings. A broad 

 dorsal stripe of some shade of yellowish brown, quite thickly flecked 

 with black-tipped hairs, is bordered by a slightly narrower lateral stripe 

 of a lighter color and usually with less black. The fur of the entire 

 upper parts is uniform plumbeous at base, only the tips of the hairs 

 affecting the external appearance of the animal. Between the darker 

 color of the sides and the white of the lower parts is a narrow stripe 

 of clear yellowish orange, unmixed with black, and with the base of 

 the hairs white. The lower parts are white, sometimes suffused with 

 the color of the sides, and one species, Z. setchuamts, from China, has 

 a well-defined brown ventral stripe. The tail is very long, usually about 

 60 per cent of the total length, and more or less distinctly bicolor, 

 brownish above and whitish below. It is thinly covered with short 

 hairs, which are longer on the terminal part and form a short pencil. 

 In two of the three subgenera the tail is conspicuously tipped with 

 white. The spring and early fall pelages differ noticeably, except in 

 members of the subgenus Napwozapux, the bright color of the spring 

 and early summer pelage becoming duller in the fall, and the dark dorsal 

 area partially obliterated. In some species, however, the dorsal area 

 is darker and more sharply defined in late summer and early fall than 

 in spring and early summer. 



The teats are normally 8, and arranged in pairs at regular intervals. 

 The pectoral pair is situated just back of the forelegs, the inguinal pair 

 far back at the base of the thighs, and the remaining pairs between. 

 Sometimes the anterior or posterior pair remains undeveloped. 



Habits. In general but one species occurs in a given locality, but 

 Zj)ttx huclsonius, which has the widest range of all, seems to be always 

 present throughout the range of the subgeuus Xap(i'o.?pus, the members 

 of which are almost invariably found in deep woods near streams. All 

 the other species delight in meadows, shrubby fields, and thickets along 



1 Preliminary report on the Vcrtebrata discovered in the Port Kennedy Bone Cave 

 <Proc. Am. Philos. Soc., XII, p. 86, 1871. 



Vertebrate Remains from Port Kennedy Bone Deposit <Jonrn. Acad. Nat. Sci. 

 Phil.-.., I'd ser., XI, p. 200, 1899. 



-Spelled hudsonianus by Zittel, Haudbuch der Paheoutologie, IV, p. 527, 1893. 



