64 DIPTEEA. 



stated, and was so far ignored, that Bigot, in his monographic essay on "Acantho- 

 meridse," has proposed a separate genus for the male sex. The only comparative 

 statement about the structure of the male and female antennae we possess is that of 

 Wiedemann (in the description of A. vittata), and that is not very clear : " beim d viel 

 kiirzer und bei weitem nicht so deutlich geringelt, als beim $ , der Endgriffel nicht 

 ein Viertheil der Lange erreichend." 



The antennas of Acanthomera consist : — 1, of the two-jointed scapus ; 2, of a flattened 

 compound joint of seven segments, the first of which is the longest ; 3, of the style. 

 In the male of many species the compound joint has the shape of a flat disc, rounded 

 at the base, more or less attenuated at the distal end; in most cases its ending is 

 abrupt; the setiform style, considerably longer than the compound joint, is inserted 

 upon it. But in other species the compound joint of the male does not end abruptly, 

 but tapers gradually into a point, which merges into the last joint, corresponding to 

 the style. A. picta, Wiedem., male, and several undescribed or unnamed species which 

 I have seen in collections have such antennas. It is very probable that species will be 

 found forming the transition between the two forms. 



The antennae of the female are very like the antennae of the second form of the 

 male, only distinctly broader; the flattened, tapering, compound joint gradually merges 

 into a long terminal joint, corresponding to the style in the male, but comparatively 

 stouter and less setiform. The sutures between the segments of the compound 

 joint are more or less distinctly marked in different species, and are characteristic 

 of the species. 



Bigot established the genus Megalemyia (Ann. Soc. Ent. Fr. 1881, p. 455) on those 

 Acanthomerw which have a disciform compound joint with a setiform style at the tip, 

 that is on specimens of the male sex only. His Megalemyia seticornis is the male of the 

 species which, in the same paper, he describes as Acanthomera rubriventris, $ , n. sp. 



Wiedemann mentions the subfemoral spine on the hind femora as a character of the 

 genus Acanthomera, and even derives the generic name from it. In reality, the minority 

 of the species only have a spine ; and among the three species described by Wiedemann 

 himself in his first volume, A. vittata has none. It remains to be ascertained whether 

 this spine is a constant character in those species in which it appears, or whether its 

 presence depends on the development of individuals, so that in some specimens it may 

 be wanting; also whether its development in both sexes is equally strong. The 

 presence of this spine is difficult to ascertain in cases when it is small and concealed 

 among the hair on the underside of the femora. In order to discover its presence or 

 absence, it may be necessary sometimes to detach the leg and to rub the under surface 

 of the femur with the tip of one's finger. This difficulty must be borne in mind in 

 identifying descriptions. 



There is another spine at the end of the femur, in a line with its longitudinal axis, 

 on the outer side; when small it may be sometimes overlooked on account of the tibia 



