1896.] NATURAL SCIENCES OF PHILADELPHIA. 533 



Skull — Total length, 19.3 rara. ; greatest breadth, 9.8 ; interorbital 

 constriction, 3; length of nasals, 7.2; length of mandible, 11.5; 

 width of mandible, 5.7. 



Two specimens of this minute mouse, both males, taken at Sheikh 

 Mahomet, appear to be undescribed. In some respects they resem- 

 ble the characters given by Riippell for Mus iniberbis, but they 

 are much smaller with relatively longer tails and have well devel- 

 oped whiskers. 



The so-called whiskerless character of Riippell's animal appears 

 to me to be an anomaly due to abnormal rather than natural cir- 

 cumstances. In any event, this question in no wise affects the 

 status of the mouse which owes to an accident of birth and locality, 

 rather than to its possession of whiskers, the august specific name 

 which I have imposed upon it. 



39. TMus arborarius Peters. Long-tailed Wood Mouse. 



Two specimens, both females, (No. 3,847, ad. skin and skull ; No. 

 3,890, juv. in alcohol), from River Darde, September 12, 1894, are 

 of interest. 



Mr. Oldfield Thomas considers" M. arborarius of Peters synony- 

 mous with M. dolichurus. If this is the case, the River Darde mice are 

 perhaps, a good subspecies characterized by the excessively long tail 

 and smaller size. In our oldest specimen (No. 3,847), with molars 

 more worn than in the adult type skull of arborarius figured by 

 Peters,^^ the skull is markedly smaller and shallower. 



After examining their descriptions it seems to me that Peters has 

 plainly set forth good distinctions between his arborarius and 

 Smuts' dolichurus. The most marked character of arborarius is 

 the jDure white feet and belly, which in dolichurus are fulvous. The 

 absence of a preocular spot in arborarius is also to be considered. 

 In these respects the Smith specimens resemble arborarius. The 

 feet and under parts are immaculate white to the roots of the hairs. 



In the adult, the total length is 100 mm., that of the tail vertebrae 

 being 150 mm. In the younger one, contrary to the general rule 

 in young murines, the proportional size of tail to head and body is 

 even greater than in the adult, the former being 122 mm. long and 

 the latter 76 mm. 



In the type of dolichurus the length of head and body is 125 mm. 

 and the tail 145 mm. In arborarius the head and body of the female 



"P. Z. S., 1891, p. 186. 



'SEeise n. Mossam., 1852, pi. XXXV, fig. 7. 



