2 
DIPTERA 
famil}' is very abundant in amber; Loew, and quite recently Meunier, have described numerous genera 
and species from the Baltic amber. The fossil genera thus far described do not differ strikingly from 
some of the recent forms, and indeed the differences in some cases are so shght that it is difficult to 
separate them. Several genera, heretofore known only as fossils, have been discovered by the writer 
among living forms, and for this as well as for other reasons they have been considered in the tables 
which follow. 
Immature stages and habits. — The larval stage of the Mycetophilida? (exclusive of the 
Sciaridae) with but few exceptions is passed in mushrooms and decaying wood. The eggs, white oval 
bodies, are laid in the soft wood or between the gills of a mushroom and develop very rapidly. The 
larvae differ somewhat in structure though superficially possessing a very great similarity. They 'are 
twelve segmented, footless, more or less cylindrical, slightlj' tapering, smooth, soft, whitish in color 
and with a small strongly cliitinized head, which is usually brown or black. The antennae are always 
very minute, almost rudimentary. The mouth parts consist of a fleshy labrum, with a chitinized frame; 
flat lamelliform mandibles, indented or serrate on the inner side; maxillae with inner and outer lobes, 
the former usually serrate, and a small chitinized labium. The body of the larva is without hair or 
biistles except that in some genera there are one or two transverse rows of simple or bifid ambulacral 
setulae on the margin of each abdominal segment on the ventral side. There are eight pairs of spiracles, 
one on the thorax and seven on the first seven abdominal segments, the last two segments having none. 
These spiracles are protected by small, chitinized conical projections. 
The pupae are extricated, that is, not encased in the contracted skin of the larva. The legs are 
applied to the breast and venter, the antennae are bent around the eyes, and extend between the wings 
and legs. The prothoracic spiracle is placed a little above the root of the wing and immediately behind 
the antenna. The abdominal spiracles are distinct on both sides of the abdomen. The pupa is smooth, 
white in color and usually encased in a delicate cocoon. The pupae of those forms whose larvae live in 
mushrooms are usually found in the soil and among the decaying parts of the plant. The larval and 
usually the pupal life also is of short duration. The time which elapses from the egg to the adult stage 
may not exceed two weeks in midsummer. 
For expediency's sake, and also in deference to the opinion of many dipterologists the Sciaridae 
are not included with the Mycetophilidae although it must be confessed they are no more remote from 
some genera of the subfamily Mjxetophilinae than the genera Diadocidia and Bolitophila, and certainly as 
near as the genera Pachyneura and Tliiras which I have included. I have also included several genera in 
my tables which probably belong with the Sciaridae but because of their transitional characters might be 
wholly overlooked were they omitted. Hitherto the wing venation has been most used for generic cha- 
racters but more attention must in the future be paid to seta arrangement, claws, palpi, ocelli, antennse 
and particularly to the male genitalia. With the discover}? of new species from the unexplored regions 
of the world some transitional forms will doubtless be found and some of the present genera will then 
have to be combined. In the present paper the fossil genera are included though their consideration 
makes the definition of recent genera more difficult and restricted. 
The only family with which the Mycetophilids as here considered ma)' be confused is the Scia- 
ridae. It differs liowever in wing venation; the R-M crossvein is parallel to the long axis of the wing and 
forms apparently the base of a longitudinal vein; the cubitus (except in some fossil forn.s) has a very 
short petiole, the subcostal vein, though usually rather long, ends free, and the media has an elongate 
but very slender petiole (PI. 6, Fig. 28, 29). The head also is placed at a higher level relatively to 
the tliorax, the thorax is less arched, and the coxae are not so conspicuously elongate. 
Family characters of the adult. — The head is narrower than the thorax, spherical or elon- 
