228 NEW YORK STATE MUSEUM 
illustrate in their different species the tendency of M! and M? 
to iuse together Limnophila toxonieuna pl 18) tio) 
shows a moderate fusion; L. brevifurca [pl. 14, fig. 6] 
shows fusion almost to the wing margin; and L. quadrata 
[pl. 18, fig. 6] shows the fusion complete; and the other 
species of Limnophila figured on plate 18 show various inter- 
mediate conditions. Rhaphidolabis [pl. 19, fig. 2] shows these 
veins almost fused, and the nearly allied Plectromyia [pl. 30, 
hg. 4] shows them wholly fused. 
In the hinder fork, 1 have seen no evidence of any tendency 
for M® and M* to fuse, but both tend to atrophy. Both, though 
commonly developed in the more generalized neuropteroid in- 
sects, have been found well developed among all the Diptera 
only in the fossil Rhabdinobrochus above cited. One of the 
hinder branches of media is quite persistent. In fact it is 
nearly always present, but it may be found well developed or 
weak or broken or absent in different species of the genus 
Dicranomyia. It is usually fused basally with vein Cu! for a 
distance, but I have never found it fused beyond the level of 
the median cross vein, and I do not believe that it ever dis- 
appears by total fusion in the Tipulidae, although it does so 
ono CEI Ox We lng IDs, IDieCramomyiz 
immodesta [pl. 27, fig. 3] shows it persistent while the 
median cross vein has disappeared, D. cinerea [pl. 27, fig. 4] 
shows it interrupted, and attached to the end of the flexed 
median cross vein, the two together simulating very decep- 
tively a persistence of vein M?. This appearance is wholly de- 
ceptive, however, aS any one may Satisfy himself by a little care- 
ful comparative study. In) Di whartoni [ply 275 nes silat 
has wholly disappeared, save for the slightest bit of a spur on 
* Critical comparative study is sometimes necessary for determining where 
vein R ends and vein M begins. In Paratropeza. [pl. 21, fig. 4], for 
example, there are five branches of veins reaching the wing margin between 
the tips of R, and Cur. Is it Rs or M that is three branched? How shall 
this be determined? Only by comparison of allied forms. It will thus be-~ 
come sufficiently clear that Rs is three branched. The other interpretation 
would be inconsistent; for (1) the first fork of the vein Rs is always 1n- 
volved in the formation of the cord; vein Ret; is here set off posteriorly at 
a right angle from the base of vein R213; and (2) in allied forms the cross- 
vein M joins at its anterior end veih Mi4s, not vein M2; that is, it is — 
situated on the proximal side, not on the distal side of the upper median 
fork. That fork is therefore not present in Paratropeza. ‘his ap- 
parent confusion is due to the elimination of the 7-m cross vein by the long 
basal fusion of veins Rits and M42. 
