432 Mr. F. W. Edwards on 
from a study of the adults the conclusion which Keilin had 
already arrived at from a close examination of the larve. 
At his suggestion I have re-examined the adult morphology 
of Ditomyia and Symmerus, in order to ascertain whether 
any characters exist which will mark off these genera sharply 
from all other Mycetophilide. The search has in this 
instance proved almost fruitless: the points of resemblance 
between these genera and the Ceroplatine are so numerous 
and important, and the distinctions between them and the 
Bibionidze so obvious, that it is difficult not to conclude that 
the two genera in question must remain within the Myceto- 
philide. If the Ditomyiide be recognised as a distinct 
family, adult morphology would indicate that at least the 
same rank should be accorded to Diadocidine, Pachy- 
neurine, Bolitophiline, and Ceroplatine. This, Dr. Keilin 
assures me, would be unjustifiable in view of larval 
morphology. 
The following appear to me to be the most important 
characters of the Ditomyine:—(1) The rather long vein 
R,,,. This is almost the only constant point of difference 
between the Ditomyine and all other Mycetophilide ; it is 
only a relative character, and therefore can hardly be used 
by itself for family definition ; (2) The vestigial subcosta, 
which in only one case reaches the costa. This provides the 
readiest distinction from the Ceroplatine, and is rather a 
surprising feature considering the decidedly primitive nature 
of the rest of the venation ; (3) The shape of the hypopleure, 
which differ from those of most of the other subfamilies 
in being much less prominent, gently rounded, and not in 
the least produced backwards. The distinction from the 
Ceroplatine in this respect is quite marked, from the 
Diadocidine and Bolitophiline less so. Another small point 
is (4), the tendency to the development of a strong bristle 
about the middle of the posterior side of the posterior side 
of the hind coxe, aud of a tuft of strong bristles on each 
side of the mesonotum just in front of the wing-base. This, 
however, is not at all well marked in the European forms. 
It may also be noted (5) that there is a tendency toa strong 
emargination of the eyes and the development of a“ bridge ”’ 
similar to that of the Sciaride, but there is no trace of this 
in the type-genus Ditomyia. 
On this definition the genera <Arctoneura, Casa, and 
Nervijuncta, placed by Johannsen in the Ceroplatinz, should 
be transferred to the Ditomyine; but, on the other hand, 
Paleoplatyura, which was placed by Johannsen in the 
Mycetobiine, will go to the Ceroplatine. 
