472 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
thick below, with very sharp upper border and straight anterior and 
posterior surfaces. The erect, silvery white hairs covering the body, 
legs, and antennal scapes are longer and more abundant. The pu- 
bescence is very fine and sparse on the gaster so that this region is very 
smooth and shining. The mesonotum is not spotted but, together 
with the scutellum, paraptera, and metanotum, uniformly dark brown 
and rather sharply marked off from the remaining paler portions of 
the thorax, which are brownish red. Occiput slightly infuscated. 
Gaster very dark brown, anal region red. Wings grayish hyaline, 
with brown veins and stigma. 
Nevada: Ormsby County, July 1903 (C. F. Baker). 
Although this form is readily distinguished from the females of all 
the forms of microgyna by its very smooth gaster, more material may 
show that it is to be regarded as a subspecies of microgyna and not as 
an independent species. 
59. F. mperexa Wheeler. 
F. impexa Wheeler, Bull. Amer. mus. nat. hist., 1905, 21, p. 273, 8 ; Psyche, 
1906, 13, p. 40, 2; Ants, 1910, p. 570. 
WorkeER. Length 3.3-6 mm. 
Resembling F. microgyna. Mandibles 8-toothed. Clypeus broadly 
rounded in front, not produced in the middle, carinate its entire 
length. Head, excluding the mandibles, distinctly longer than broad 
even in the largest workers, with straight posterior and straight, 
subparallel lateral borders. Joints 1-4 of funiculi decidedly longer 
and more slender than the penultimate joints. Maxillary palpi rather 
short. Thorax with the epinotum low and much rounded, without 
distinct base and declivity, mesoépinotal constriction rather narrow 
and shallow, pro- and mesonotum moderately convex. Petiole nar- 
row, cuneate in profile, its anterior surface convex, its posterior surface 
flat, its border moderately sharp and produced upward in the middle. 
In small workers the edge may be much more blunt. 
Mandibles lustrous, finely and sharply striated. Surface of clypeus 
uneven. Frontal area smooth and shining. Remainder of body 
opaque, finely but distinctly shagreened. 
Whole body and appendages clothed with very minute white pubes- 
cence, which is rather sparse on the head and thorax, but dense and 
concealing the ground surface of the gaster. Body, antennal scapes 
and legs covered with short, coarse, obtuse, erect or suberect, whitish 
or yellowish hairs. On the gaster these are uniformly distributed 
and in certain lights very conspicuous, but shorter than in the various 
forms of microgyna. They are also very numerous and prominent 
