BANGS: CHIRIQUI MAMMALIA. 27 
Among tree squirrels, Syntheosciurus brochus has no very near ally; its 
light, papery skull recalls that of Sciuropterus, but the audital bullae are much 
smaller, Its peculiarly straight, slender rostrum, weak, projecting, and 
grooved incisors at once distinguish the genus from any other. 
Mus rattus Linn. 
One youngish 9, Boquete, 4,800 ft. Mar. 
Megadontomys! flavidus,? sp. nov. 
Type. — Mus. Comp. Zool. No. 10,331, ad. &, Boquete, April 12,1901. 4,000 ft. 
Twenty-seven specimens, Boquete, 3,000 to 5,000 ft., February and April. 
Characters. — A large species, much paler and yellower than M. thomasi 
Merriam, Mountains near Chilpancingo, Mexico, 9,700 ft., and M. nelsoni 
Merriam, Jico, Mexico, altitude 6,000 ft. ; skull with much more rounded and 
elevated and less flattened brain case; palatal slits very wide ; audital bulle 
decidedly small; ears small. 
Color. — Upper parts brownish cinnamon, usually rather more rusty toward 
rump, brighter, inclining toward orange-buff along lower sides; a large, con- 
spicuous blackish patch on each side of head at base of whiskers; whiskers 
mixed black and colorless; underparts white, the gray basal portion of the 
hairs showing through ; a slight collar yellowish or buffy; feet and hands 
whitish, marked with brown about ankles and wrists; tail sparsely clothed 
with short stiff hairs, dusky above, grayish below; ears nearly naked, dusky 
outside, slightly silvery inside. Young examples differ from the adults in be- 
ing darker and duller brown above ; the under parts more grayish, less purely 
white. 
Measurements (of ten adults, type and topotypes) — 
No. Sex. Total length. Tail vert. Hind Foot. Ear. 
10,327 & old ad. 375 205 31 23 
10,329 & old ad. 355 195 32 23 
10,333 & old ad. 350 185 32 24 
~ 10,339 & ad. 345 185 32 22 
10,336 & ad. 345 187 32 23 
10,331 type ad. 336 180 31 23 
10,328 & ad. 335 155 32 20 
10,338 & ad. 330 185 32 22 
10,342 od ad. 325 170 Bu 23 
10,330 Oiiad. 320 165 33 22 
1 Though described by Dr. Merriam as a subgenus of Peromyscus, Megadontomys 
is entitled to generic rank, on account of the unwieldy proportions of Peromyscus. 
2 Flavidus, yellowish. 
