460 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxvl 



MUS SURDUS, new species. 



7>/^;^.,_ Adult imilc (skill and skull), Ciit. No. 114184, U.S.N.M. 

 Collected on Simalur Island December 11, 1901, by Dr. W. L. Abbott. 

 Original number, 1359. 



Chivmcter^. — Similar to Mus concolor Blyth and Mm jyullus Miller, 

 but larger and paler. 



Fur and external characters in general. — The fur, tail, ears, feet, etc., 

 are as in Mus concolor and Mus pull us. Mammae, i. 2-2, p. 2-2=8. 



Color. — Back and sides a coarse, inconspicuous g-rizzle of dull ochra- 

 ceous buff and blackish brown, the former slightly in excess on back 

 and distinctly predominating- on sides. Underparts and inner sur- 

 face of Hmbs dirty white, tinged with cream buff. In the type there 

 is a fairly well defined line of demarcation between the color of sides 

 and that of belly. This contrast, though not always so conspicuous, 

 is invariably more noticeal)le than in the type of Mus pull m or the two 

 specimens of Mus concolm^ that I have examined. Ears blackish brown 

 externally, lightly sprinkled with fine, silvery hairs internally. Feet 

 dirty whitish. 



Skull and teeth. — Both skull and teeth are noticeably larger than in 

 Mus concolm' and Mus pullus., but I can detect no tangible difference 

 in form. 



Measurements. — External measurements of type: Total length, 265; 

 head and body, 127; tail vertebrtv, 138; hind foot, 28 (26). Average 

 of 21 adults from the type locality: Total length, 268 (238-321); head 

 and body, 130 (112-143); tail vertebra?, 139 (119-182); hind foot, 27 

 (26-28.2); hind foot without claws, 25.4 (24-27). For details see 

 table, page 461. 



Cranial measurements of type: Greatest length, 33 (30);" basal 

 length, 28.6 (26); basilar length, 26 (23); diastema, 8.8 (8); length of 

 incisive foramen, 6.4 (5.4); combined breadth of incisive foramina, 2.8 

 (2); length of nasals, 12 (11); greatest combined breadth of nasals, 3.4 

 (3); zygomatic breadth, 15.4 (13.6); least interorbital breadth, 5 (4); 

 breadth of l)rain case above roots of zygomata, 13.6 (13); depth of 

 brain case at front of basioccipital, 9.6 (9); frontopalatal depth at pos- 

 terior extremity of nasals, 7.4 (fi-'o); mandible, 18.8 (15.4): maxillary 

 tooth row (alveoli), 5.6 (4.6); mandibular tooth row (alveoli), 5.6 (4.6). 



Specimens examined. — Thirtj^-two (11 in alcohol), all from the type 

 locality. 



Rt'inar'ks. — Though closely related to Mus concolor and Mus indlus 

 this species appears to be well differentiated. Like Mus simalurensis 

 it probably owes its introduction and therefore its existence to prehis- 

 toric man. 



"Measurements in parantheses are those of the type of Mm pullus. 



