MDBID^— 8IGHODONTES-NBOTOMA CINBBBA. 



27 



ones form a brush two inches beyond the end of the vcrtebroe. This maxi- 

 mum of hairiness, however, is rarely if ever seen, except in borjal specimens : 

 the most hcavily-iiaircd United States tails are only about tvo inches across; 

 an average one is rather less than this; the average pencil at tlie cn<l is prob- 

 ably not over one inch. There is a great difTerence, also, according to season. 

 In the spring, when the animal has just lost its lieavv winter-coat ; and in 

 summer, l)el'ore it has commenced to put on its protection from the cold, the 

 tail may bo only a little more hairy than in Kansas samples of N. Jloridana. 

 Thus, in Nos. 3897, 3898, 9324, &c., the hairs aro much less than an inch 

 across, along most of the tail ; and this member looks precisely as figured i)y 

 Audul)on. Comparison of Audubon's with Richardson's plates will give an 

 excellent idea of the extreme dilFerences ; both these figures are faithful, and 

 can be precisely matched in our series. It is hardly necessary to add that, 

 nevertheless, the tail is never so scant-haired as to permit the annuli to be 

 seen. - . ■ 



The ears, and to some extent the feet, share the general increase of hair- 

 iness OS er Jloridana that the tail shows. The ears are, in general, closely and 

 softly pilous, much like a squirrel's ; never so nearly naked as m Jloridana, &c. 

 In United States specimens, there is riot much difference in this respect ; but, 

 in the arctic ones, this soft pilous strife becomes actually hirsute. In all the 

 specimens, the heels are closely hairy to the posterior tubercle ; in arctic ones, 

 the hairiness is more dense, and even encroaches on the sole from the sides. 

 The hairs on the upper surfaces of the toes generally reach about to the ends 

 of the nulls; in arctic examples, they are longer, completely hiding the 

 claws. The palms are always completely naked from the posterior tubercles. 

 The tubercles are five in number: two abreast, posterior; two abreast at base 

 of 5th and 2d toes, respectively; one intermediate between tiiese last and a 

 little anterior to them at conjoined bases of 3d and 4th digits. The very 

 rudimentary 1st digit looks exactly like an additional tubercle at the antcro- 

 intenial corner of the inner posterior one. The soles have six tubercles, 

 with ihe ordinary disposition ; the posterior one of these is subcircular (not 

 linear, as in Mus, &c.). 



Aside from seasonal conditions, which, being well known, and the same 

 as in other rodents, need not be here particularized, the pelage varies in the 

 series as follows : The arctic skins are very full-haired and soft ; the United 

 States prairie-region skins are equally soft, if not more so, but not so full ; 



