Systematic Position of the Genus Mycetobia, Mg. 115 



Other Characters. 



As regards the other cliaracters — those of tlie thorax, 

 abdomen, a!id legs, — not much need be said. Rhi/phus is 

 peculiar in having holoptic eyes in the male and greatly 

 enlarged empodia ; it does not, however, share either of tiiese 

 characters with Olbiognster, which resembles the Myceto- 

 PHiLiDiE rather than lihijphus in both these respects. 



Of the male genitalia, which usually provide sound indica- 

 tions of relationship, I have made no comparative study ; 

 but it is noteworthy that Mycetohia appears to be the only 

 Mycetophtlid which possesses cliitinous ppermathecse in the 

 female. Ot' these, tliere are two in Mycetohia, two (or, 

 perhaps, three) in Olbiogaster, one in Rhyphus. 



Conclusions. 



1. Mycetohia agrees with the Rhyphid^ and diverges 

 from the Mycetophilid^ in the possession of a large guiar 

 plate, in the structure of the second palpal joint, in the 

 position of the forking of the radial vein, the course of the 

 cubital vein, and in the chitinous spermathecas of the female. 

 Since the venation of Mycetohia has been shown to be 

 directly derivable from that of tlie Rhyphid genus Olbioyaster^ 

 it is probable that any resemblances in this respect to the 

 Mycetophilid^E are due to convergent evolution, and not to 

 relationship. The genus Mycetohia (and with it Mesocliria, 

 though not Ditomyia ox Synimerus) must therefore, on grounds 

 of adult as well as larval structure, be transferred from the 

 Mycetophilidjl to the Rhyphid^. 



2. It is at least possible that the characters of the gular 

 plate and of the position of the radial fork will be found on 

 full investigation to divide the Nematocera into two groups, 

 and there is evidence that these groups may coincide with 

 those founded on other characters, notably the tracheal system 

 of the larva ; this evidence, therefore, tends to confirm Knab's 

 recent division of the Nematocera (Ann. Ent. 8oc. Anier. 

 vol. viii. p. 93, March 191.5) into Oligoneuiu, with peri- 

 pneustic larvse, and PolyneurA, with ampliipneustic larvje. 

 The genus Pachyneura seems to require special study, owing 

 to the intermediate character of its venation, and Eupeitenus 

 is also aberrant. 



3. If, as seems probable from many considerations, the 

 higher Diptera have been derived from the I\)LYNEUKA and 

 the OliGONEURA represent an entirely distinct line of evolution, 



. 8* 



