24 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 
Seiurus (Microsciurus) browni,' sp. nov. 
Type. — Mus. Comp. Zodl., No. 10,404, old ad. @ Bogaba, July 15, 1901. 
Five specimens, both sexes, Bogaba, July. 
Characters. — Probably nearest to S. alfari Allen, from Costa Rica, but dif- 
fering in many respects from that species. Pelage much thinner, less woolly; 
upper parts decidedly more olivaceous — lacking the reddish brown of S. alfari; 
tail thinly washed with grayish white instead of dull rusty ; nose, forehead, 
and orbital ring more tawny ; under parts much paler ; in the new species dull 
gray slightly washed with buffy in some specimens, yellowish white in others, 
on under side of neck and middle of belly, in S. alfari the under parts are dull 
rusty on under side of neck and breast with a thin wash of this color extend- 
ing back over belly, which has a dull brown shade. 
The skull is similar to that of S. alfari, but the brain case is narrower, more 
rounded and without so marked a constriction in front of the occiput, and with 
the mastoid region less prominent. 
Color and Pelage. — Pelage short and thin, rather harsh and with but little 
under fur. 
Upper parts, a fine mixture of tawny olive and bistre, produced by the dark 
brown bases and tawny olive tips of the hairs; nose, forehead, and orbital ring 
tawny ; tail with the hairs dark reddish brown basally then black and tipped 
with grayish white, a small black pencil ; under parts dull gray to grayish 
white, slightly washed with buffy or yellowish (in some specimens, very slightly 
in the type) on under side of neck and middle of belly; under sides of legs 
darker — more nearly like upper parts. 
Measurements — 
No. Sex. Total length. Tail vert. Hind foot. Ear. 
10,404 type ¢@ ad. 260 120 38 14 
10,405 9 ad. 255 100 38 14 
10,407 9 ad. 232 110 38 13 
10,406 9 ad. 250 110 36 14 
10,408 ¢@ youngish 245 110 37 13 
Skull, type, adult 9, basal length, 29; occipitonasal length, 36; zygo- 
matic width, 21.2; interorbital width, 12.4; palatal length, to palatal notch, 
13.4; to end of pterygoid, 20.2; length of nasals, 11; length of upper molar 
series, 5.8. 
Remarks. — Mr. Brown found this little squirrel in the forest about Bogaba, 
at 600 feet altitude. It was rare and exceedingly hard to get, on account of 
its small size and dull coloring, and only by devoting much time and energy 
to the chase did he succeed in taking five specimens. 
Mr. E. W. Nelson has compared very carefully these five specimens with 
the type of Microsciurus alfari Allen, and agrees with me as to the specific dif- 
ferences between these two tiny tree squirrels. 
1 Named for Mr. W. W. Brown, Jr. 
