346 THE AMERICAN NATURALIST.  [Vot. XXXV. 
across the abdomen; the second, four times as wide as long, oval; the 
third, similar and much smaller; fourth, triangular, with a large pit in the 
center. Sexual organs of the usual form. The central axis is broadly 
rounded and bisetose at tip; lamella short, club-shaped, and rounded at 
the tips, quite bristly. Last two abdominal segments with rows of marginal 
bristles. The last two segments of the abdomen are retractile, as in Ecitomyia, 
and capable of being exserted to a considerable extent. Legs moderately stout. 
Hind metatarsi flattened, and with regular rows of transverse macrochete. 
Three female specimens found in a nest of Solenopsis geminata Fabr., 
at Austin, Texas, Oct. 24, 1900, by Dr. Wm. M. Wheeler. 
The structure of Commoptera is on the whole more degen- 
erate than that of Psyllomyia. The eyes are larger and the 
ocelli present, but the swollen membranous abdomen and 
general habitus are at least a greater departure from the 
phorid type, if not a mark of degeneracy. 
The head and its appendages are much as in the genera 
described by Wandolleck. The eyes are, however, less reduced 
and the ocelli nearly of normal size. A most remarkable dif- 
ference is seen in the proboscis, which is not long as in Psyllo- 
myia. The mouth-parts do not differ to any extent from those 
of some Phoras which I have examined. 
The thorax and its appendages present nothing new, except 
the peculiar condition of the wings. At first I thought it 
possible that the wings were normally of the usual size and 
had been bitten off around the edges. But this view is dis- 
proved by two facts. In the first place, the wings are sym- 
metrical and have the edges perfectly continuous. In only 
two wings (out of six) did there seem to be any irregular or 
notched places along the posterior margin. Secondly, the 
extreme activity of the flies would make it impossible for 
the Solenopsis, although it is quite an active ant, to gnaw off 
the wings soas to present even a semblance of the perfect sym- 
metry exhibited. We are then forced to conclude that such 
abortion is natural and that the wings have been decreased in 
size on account of the inconvenience they presented to the fly 
while moving about in the galleries of the Solenopsis nest. 
Wings would indeed be a great inconvenience in moving about 
in the narrow galleries and quite an unnecessary burden, when 
the legs are adapted to such wonderfully quick motions. 
