4f^8 PROCEEDIKOS OF U.MTEl) STATES NATIONAL MUSEUM. [1885. 



ish hairs, the latter best nmrked on ihc dorsum, becoming less so as we 

 approach the sides. Sides bright fulvous. Entire under parts white, 

 blending with the fulvous of the sides, the line of demarcation being 

 by no means so eA'ident as rn //. JeucoiniH. Upper sides of feet white. 

 Tail bicolor; upper side blackish brown, white beneath. Manns and 

 pes agree with H. leucopus. 



Dental characters. — In the dental formula, as well as the method of 

 implantation of the teeth, this animal agrees with H. leucopus., but in 

 this, the type specimen, the crowns of the molars are peculiarly worn 

 away, as described above. It will be interesting to examine other spec- 

 imens with the view of looking into this subject, ascertaining, if possi- 

 ble, how far this condition is constant, and to what extent it may be 

 due to age. 



Cranial characters, — Although the skull presents in general the char- 

 acters of the genus, it is considerably longer and larger in other ways 

 than the skull of H. leucopus. (See table.) This increase in size has 

 not been accompanied by an increase of strength or thickness of this 

 structure; on the other hand, if anytliing, the skull of True's mouse is 

 of a more attenuated and delicate composition than that of the com- 

 mon white-footed mouse. The basioccipital is more emarginate also 

 than in that species, and the periotic is quite different in form. 



In the mandible we Und that the sym})hysial portion is not bent np 

 so abruptly as it is in all forms of H. leticopiis^ and in consequence the 

 lower incisors are directed about equally forwards and upwards, while 

 in R. leucopus these teeth are, in most specimens, curved almost en- 

 tirely upwards. (Figs. 7 and 8, i)l. XXI.) 



The skeleton of H. Truei presents many characters, apparently of 

 specific value, by which it may be distinguished from that of H. leuco- 

 pus. The manubrium of the sternum is shorter in the former sj)ecie8 

 than in the latter; the anterior margin of the scapula is larger and 

 more sharply angulated, and the posterior margin straighter ; the pos- 

 terior margin of the pelvis is much more rounded ; the transverse proc- 

 esses of the lumbar vertebrae are more slender, and those of the sacrals 

 wider. 



True's iiiiion mouse differs then from the common white-footed mouse, 

 H. leucopus, in the fact that it chooses a different character of the 

 country where it is found, as its home; in its more robust form ; in its 

 extraordinarily large ears ; in important cranial and skeletal characters; 

 and in a very marked degree in general coloration, though less weight 

 is to be attached to this last diflfeience than to any of the others. 



At present little or nothing is known of the habits of this mouse; 

 in these, however, it probably largely agrees with other field mice. 

 Living in the mountainous and piiioncovered belts of this region ; 

 building its nest in the hollow trunks of trees ; subsisting upon such 

 food as the country would afford a small rodent, and hibernating dur- 

 ing the winter months. 



