THE MYCETOPHILID^. 93 



although some good work has been done recently on the Continent, 

 especially in Russia. Verrall has not worked this family yet, so the 

 British list is far from complete ; nevertheless, forty genera and about 

 160 species are recorded, and many reputed. Alany of the species 

 described by Walker must be eradicated, as in all the other families, 

 with the exception of the DolichopodidiC. 



Few insects are more abundant than the "fungus gnat," but their 

 appearance is so extremely erratic that one may go a whole year and 

 find none, then hundreds may suddenly appear. They seem to have 

 been first discovered in the Purbeckian Period, and many genera 

 have been obtained from these Mesozoic beds, including Platyura, 

 Sciophila and Macrocera {vide Brodie's "Fossil Insects"), from the 

 lower Purbecks of Wilts and Hants. From the Solenhofen States 

 Germar* describes a Sciara, S. prisca^ and one also by Giebel.f 

 The three genera figured by Brodie are given by Giebel as new 

 genera, viz., Adonia, Saiiia, and Thimna respectively. Besides these 

 Westwood also figures an obscure species referred to the extinct 

 genus Thiras. When we come to the Tertiary Period we find large 

 numbers of these "gnats," which are represented by the genera 

 Zygoneura, Mycetophila, La'a, Sciara, Sciophila, Sciobia, Platyura, 

 Macrocera, Heterotricha, Diancpsia, Mycetobia, Aclada, Diadocidia, 

 Boletophila, Cordyla, Brachypeza, Tricliotita, Boletina, Gnoriste,X 

 and an extinct genus Sackcnia ; more than 280 species have been 

 found, and from widely separate areas, mostly from the ambers of the 

 Continent and from America, the rock species being few compared 

 to the amber. 



Their range in time is seen to be fairly wide, as also is their distri- 

 bution in space, for the fungus gnats appear in most parts of the 

 globe, from Scandinavia into the tropics. They pass into the Arctic 

 circle, cold seeming to have no influence on them. For some time 

 I kept the pupse of some AlycetophilidiC in a temperature of 30°, the 

 effects of the cold only retarding the development a few days, and 

 in no ways injuring the species. In England several species may be 

 taken in the middle of winter. 



The habitat of the imagos is generally amongst the grass and in 

 hothouses, where they may sometimes be taken in great numbers on 

 the glass. They also often appear in great numbers on windows in 

 houses, and I have noticed this especially during the autumn. One 

 of the most notable points in the habits of these gnats is the peculiar 



* Germar, ' Nova Acta,' Ac. of Leo. Ch. of Austri.i, 1S39, xix. 2, S, 189-222. 



+ Fauna der Vorwelt. Giebel. 



X Edin. New Phil. Journal, 1829, pi. vi., figs, 8, 9. 



