866 CHARLES PauL ALEXANDER 
unites with M+» for a short distance, obliterating the medial cross-vein. 
In some genera — Bittacomorpha (Plate XXX, 3), Bittacomorphella 
(Plate XXX, 4), Hexatoma (Plate XXXVI, 112), Diotrepha, and many 
species of Trentepohlia — but one branch of the media reaches the wing 
margin, and in these cases the posterior branch has either fused with 
the cubitus (as in Hexatoma) and reaches the margin by this fusion, 
or has been lost by atrophy. Needham (1908:227—229) believes the 
posterior branch of the media is lost only by atrophy, and undoubtedly 
this is true in most instances; the series of Polymera, however, a tropical, 
American genus studied by the author (Alexander, 1913 b:526-535), 
showed an interesting condition indicating that the veins may be united 
by fusion, and similar conditions may exist in the genus Rhaphidolabis 
and in the South African species Gonomyia brevifurca. The entire end of 
M; is lost by atrophy in four known species of Dicranomyia, one of these 
being D. whartoni (Plate XX XI, 15). The cell /st M2 (discal) is m many 
cases opened by the atrophy of part of Ms, leaving the tip of M; attached 
to the medial cross-vein (as in Ormosia, Plate XXXIV, 59-64, and 
in Gonomyia, Plate XXXVI, 92 and 93); in other cases it is the medial 
cross-vein (m) that is atrophied, opening the cell (asin Dicranomyia, 
Plate XXXI, 14 and 16, in Cryptolabis, Plate XX XVII, 101, and in 
many genera of the Pediciini, Plate XLI, 172-174). 
The cubitus (Cu, fig. 128, a), lying between the media and the anal veins, 
is the most constant and, after the radius, the most powerful vein of 
the wing. There are always two branches, which are never lost. At the 
fork, the anterior branch, Cw, is directed strongly forward, so that in 
all but the most generalized forms it simulates a cross-vem and from 
its conspicuous size it has long been termed the great cross-vein; this 
deflection is the basal deflection of Cu of the Comstock-Needham system, 
and the pars ascendens of Bergroth. In the more generalized groups, 
such as Tanyderidae (Plate XXX, 1), Ptychopteridae (Plate XXX, 2-4), 
a very few Limnobiinae —as some species of Tricyphona (Plate XLII, 
184 and 185) —and many of the Tipulinae (Plate XLIII, 195-197), the 
medial-cubital cross-vein (m-cu) is persistent, but in the great majority of 
cases it is lost by the fusion of Cu, and M;+.4. As already stated, this 
fusion may be very short —merely a point of contact (punctiform), a 
in most species of Tipula (Plate XLVI, 222) —or it may be subequa 
in length to the cell 1st M2, the deflection of Cu, entering the media a 
