114 Mr. F. W. Edwards on the 



at, and tlie following points of resemblance between the two 

 genera become more appartMit : — (1) the radial sector forks 

 basallv to the R-]M cross-vein, or, in other words, the small 

 cross-Vein is situated on the third longitudinal vein, instead 

 of on the prrofurca ; (2) the lower branch of the cubitus is 

 distinctly sinuous, the cell Cui having a convexity on the 

 lower side towards the base. The resemblance between the 

 venation of Mycetohia (fig. 5 a) and Olhiogasler (fig. 5 b) is in 

 some respects still more marked, and it is worthy of particular 

 notice that in Olhiogister africaniis, Edw., and still more 

 consi)icuonsly in 0. sackeni, Edw., the lowest of the three 

 veins arising from the discal cell (M3) is less strongly 

 chitiiiized than the other two, suggesting that the venation of 

 Mycetolda has arisen directly from that of Olhiogasler through 

 the obsolescence of M3. 



In almost all other MycetOPHILID^ tlie radial sector, when 

 it forks at all, does so nearer the wing-apex thati the position 

 of the R-M cross-vein, whicli, besides, is usually sloping, and 

 not straight as it is in Mycetohia. The only exception to this 

 rule is the genus Pachyneura^ in which the radial sector forks 

 exactly at the R-M cross-vein. In all other MYCETOPliILIDiE, 

 with the exception of Z(f'io»f?/ia {Glaphyroptera) and its allies, 

 the cell Cui is concave instead of convex on its lower margin. 

 Dilomyia and Symmerus, genera which, together with Myce- 

 tohia^ have been made to form the subianiily Mycetobiin^, 

 ao-ree in both tiiese respects with the other Mycetopiiilidji, 

 and I therefore consider that they are not at all closely 

 related to Mycetohia. The genus Mesochria, recently described 

 from the Seychelles Islands, is, on the other hand, closely 

 related to Mycetohia. Its venation is very interesting, as the 

 media is evanescent ; it evidently represents a further stage 

 of evolution from Myctuhia^ in which the lowest branch of the 

 originally three-branched meiiia has already disappeared. 



A comparison with other Diptera as regards the position 

 of the radial I'ork reveals the fact that in the Tipulidee, 

 Culicidfe, Fsychodida", Orthorrhapha Brachycera, and 

 Oyclonhapha it always takes place anteriorly to the R-M 

 cro.*s-vein, whereas in the Chironomidse, Simulidre, and 

 Bibionidae the radial sector is usually simple, but wiien it 

 forks does so beyond the R-M cross-vein. An apparent 

 exception to this rule, however, is the Bibionid genus JEupei- 

 tenus. It is also noteworthy that in the families of the 

 first group the media is primitively three-branched, while in 

 those of the second it is never more than two-branched. 



I 



