88 THE AMERICAN NATURALIST. (VoL. XXXVI. 
and more tapering hairs, which, however, do not form a conspicuous beard 
as in the other North-American species of Pogonomyrmex. Thoracic dor- 
sum and pleurz covered with coarse reticulate rugze, enclosing more finely 
reticulate rugose and confluently punctate, polygonal areole. In some 
specimens the rugze have a transverse trend on the pronotum and a slightly 
longitudinal trend on the meso- and metanotum ; promesonotal suture usu- 
ally indistinct. Epinotum armed with two pairs of rather blunt spines, 
scarcely longer than the breadth of their bases; anterior pair connected 
with each other at the base by a transverse ridge and with the spines of the 
posterior pair on either side by a longitudinal ridge; the space thus 
enclosed is subglabrous and traversed by a few longitudinal ruge. Hairs 
covering the thorax short, 
subobtuse, and perfectly 
erect. Stem of petiole 
laterally compressed, 
slender, provided below 
near its insertion with a 
small but distinct tooth ; 
node scarcely longer than 
the stem, its apex obtuse 
in profile, its dorsal sur- 
face subelliptical, covered 
with coarse reticulate rugæ like those of the thorax, but bearing somewhat 
longer and more pointed hairs.  Postpetiole campanulate, subdepressed 
dorsally, with a prominent rounded projection below near its base ; sculpture 
decidedly fainter than that of the petiole and consisting of rather indistinct 
rugz interspersed with punctate spaces. Gaster small, smooth, and shining 
throughout, without basal stria and punctures, and covered with prominent, 
 suberect hairs. Legs glabrous, clothed with suberect hairs. 

Fic. 2. — Pogonomyrmex imberbiculus n. sp. Worker. 
ri iew. 
While P. tmberbiculus is very sharply distinguished from any 
of the other North-American species of Pogonomyrmex by its 
small size, peculiar sculpture, and the lack of the beard of long 
hairs which suggested the generic name to Mayr (68, p. 11), it 
is, singularly enough, very closely related both in these and 
other particulars to a Brazilian species, P. negelit Forel ('86 
pp. 4, 5). Through the kindness of Professors Forel and 
Emery, who have sent me specimens of the Brazilian form, I 
have been able to compare the two species, which at first sight. 
_ would almost certainly be confounded. More careful examina- 
_ tion, however, reveals the following differences: In negelit the 
~ gaster is of a distinctly darker color than the head and thorax, 
= and its extreme basal portion is longitudinally striated and finely 

