
378 THE AMERICAN NATURALIST. 
structure. It has been placed in a different genus on account of 
the different shape and chzetotaxy of the head, its shorter thorax 
with broader dorsum, abdomen with first dorsal plate present 
and fourth wanting, and with the four rows of large spines. 
We must of course expect to find a greater disparity between 
these greatly degenerate forms than among more specialized 
Diptera, but to include two such dissimilar species in the same 
genus is hardly consistent 
Re ME with the importance usu- 
GAL ally laid upon structural 
characters. 
The head is very 
strongly arcuate in front 
and the lower margin is 
not visible from above. 
The antennz are larger 
than in the other genus, 
and the eyes slightly 
smaller. The thorax is 
not so unusual in shape, 
although the pleurz are 
slightly visible from above on the posterior part. The thorax in 
both genera is, however, a closer approach to the typical dipteron 
thorax than that of Ecitomyia. The rows of closely placed 
abdominal spines are an unusual development, which give the 
abdomen a most peculiar appearance. In this form the opening of 
the abdominal gland is near the middle of the fourth segment. 

Fic. 7.— Xanionotum hystrix Q sp. nov. 
13. Ecitomyia wheeleri Brues.! 
This form is an habitual nest mate in most of the Eciton caecum 
nests which we have seen in this region, although the imagines 
. become rare and perhaps disappear entirely upon the approach 
.. of the summer heat and drought. : 
—— The two specimens from a nest of Eciton schmitti Em. may 
possibly have represented another closely allied species, but were 
unfortunately sectioned before it was recognized that numerous 
Species of myrmecophilous Phoridae occur in this region. 
- DE -l American Naturalist, May, 1901. 


