252 
NORTH AMERICAN MYRMOSIDAE 
Myrmosa (Myrmosula) parvula Fox, (f. 
Georgia: Atlanta, August 2, 1913, 1 d', (the author), [Cornell University]- 
Illinois. Montana. 
M3rrmosa ruflventris Blake, cf- 
Nevada. 
BRACHYCISTIS Fox 
A study of the males of the genus Brachycistis reveals the 
existence of numerous unsuspected, and in some cases very well 
marked, characters for the separation of many of the species. 
The best of these characters are to be found in the genitalia, and 
especially is this true of the group of species allied to castanea, in 
which the genital characters are very strongly marked. Exter- 
nally visible and striking differences led me to make dissections 
of these organs in most of our species, with fortunate results, 
although in the major series of species there is quite a uniformity 
of structure. It is in these species that other structures are in 
general more monotonous, and good structural specific characters 
that can be readily formulated, difficult to find, while in those 
with the striking genitalic differences, correspondingly strong 
peculiarities of other structures are frequent. In other words 
the latter doulitless represent well established, distinct and sta- 
ble species, while the former represents the greater mass of 
evolutionarily more active, plastic, and less firmly established 
species. It is not surprising in such forms to find a lack of 
stability, even in characters that in the former group seem to be 
entirely fixed and thoroughly dependable for denoting specific 
limits. 
The purpose of the present task has been to study the types of 
the existing species, with a view to establishing characters that 
would make their specific differentiation definite, and to describe 
and include such additional species as are represented in the 
material before me. From the previously existing keys it is not 
possible to identify some of the type specimens themselves, and I 
believe considerable confusion and misidentification must have 
resulted from their use. Interesting as the task would be, the 
limits of time have not permitted an attempt to study the large 
amount of material of this genus that must exist in the various 
collections in this countiy, nor has any special attempt been 
