26 
Psyche 
[February 
ers of L. acervorum and Harpagoxenus both have eleven-jointed 
antennae. The importance of this lies in the fact that the sub- 
genus Mychthorax, to which acervorum belongs, is the only one of 
the holarctic subgenera of Leptothorax which exhibits this charac- 
teristic. Furthermore, in both Mychothorax and Harpagoxenus 
there is an impressed mesoepinotal suture. Since the combina- 
tion of these two characters is the criterion by which Mychothorax 
is separated from all the other subgenera in the group, their 
occurrence in Harpagoxenus leaves little room for doubt as to the 
close relation of the two genera. 
The similarity between the males of H. sublcevis and L. 
acervorum was close enough to confuse even such a careful ob- 
server as Adlerz. (96). Unfortunately it has not been possible 
to examine the male of sublcevis but a comparison of Adlerz’s 
figure with the male of acervorum showed differences which are 
rather surprising in the light of that author’s statement. In H. 
americanus there are even greater differences. Nevertheless 
these insects show a sufficient number of similar characters to 
justify the view that Harpagoxenus has been derived from My- 
chothorax. The males of both genera have twelve- jointed an- 
tennae and in H. sublcevis the shape of the joints is almost identical 
with that of L . acervorum. Curiously enough except for the 
number of joints, the antenna of H. americanus resembles that 
of L. longispinosus rather than acervorum. The mandibles of H. 
sublcevis are similar to those of L. acervorum in that they are 
toothless and so short that they do not meet. The mandibles of 
H. americanus are longer, toothed and mucronate at the tip. 
In regard to petiolar structure H. americanus more closely ap- 
proaches L. acervorum than does sublcevis. Neither of the former 
possess the ventral tooth which arms the second node of the 
petiole in H. sublcevis. It is interesting to note that the second 
petiolar node in L. acervorum is somewhat expanded laterally, 
since the squamiform second node is a marked characteristic of 
Harpagoxenus. Allowing for the minor variations which occur 
within the species, the anterior wing venation in the males of the 
two genera is practically identical. The hind wings of H. amer- 
icanus are veinless, but those of sublcevis and acervorum are cor- 
respondingly veined. 
