THE MYCETOFHILin.E. 105 



B. Brachial vein and cubital forming a petio- 

 late fork, 



a. Base of this fork is nearer to the base 



of wing than is base of second hind 



areolet. Diiomyia. 



b. Base of this fork is more distant from 



base of wing than is base of second 



hind areolet. Plesiastina. 



The other three British sub-families only contain a single genus. 

 The above synopsis is compiled from Winnertz, whose knowledge of 

 the Mycetophilidse is unequalled, although, as we shall see, very 

 much has recently been done in Russia, especially by Dziedzicki. 



Before ending the general account and classification of the fungus 

 gnats, one word for their preservation. If, as mentioned in a former 

 page, they do a certain amount of damage to mushrooms^ the amount 

 done is small compared with the benefits derived from their exist- 

 ence. The larvae of these gnats act as " scavengers "; not only do 

 they do away with rotting fungi, but they cause these often injurious 

 productions to putrefy and to become scarce by their destruction. I 

 have seen large fungi on chestnut trees that were gradually increasing 

 in number, until one of nature's balancers came to the fore. The 

 fungi, the first year of the attack of these Alycetid larvse, decayed 

 sooner than usual, and after that year they gradually decreased, until 

 now scarcely any are to be found. This work was done, then, by 

 these larvae, which were abundant in most of the fungi, and from 

 which I bred several species of Mycetids ; had the production of the 

 fungi continued at their rate of increase the trees must certainly have 

 suffered. We now pass on to the more detailed part of the subject, 

 and commence with the sub-family Scian?ia:. 



Genus. — Sciara, Mg. 



(Chironomus, F. 

 Bis tea, F. 



Molobriis, Macq. Lat. 

 Tipida, Lin. 



The members of this genus are small, and generally dark in 

 colour, elongated and attenuated posteriorly. The antennae are 

 porrect, i6-jointed, and have a few short hairs on each joint, the two 

 basal joints devoid of hair. Five longitudinal nerves to the wings, the 

 third forked and branching from the second about one-third from the 

 base; wings longer than abdomen. Palpi curved downwards, 3 or 4- 

 jointed. Proboscis large in proportion to the head ; the labium is a 



