862 DIPTERA OP AUSTRALIA, 



flagellum are subject to slight modifications ; the last two, three or 

 four branches on the flagellum diminish in length, the last one or 

 two sometimes a mere tooth or very rudimentary ; the terminal 

 simple joints vary from 2 to 7, generally mote in the 9 than in 

 the (J, the last of all is usually cylindrical and longer than the rest. 

 Westwood's division of the species into two sections based upon the 

 number of branched flagellar joints is useless, and was evidently 

 the result of the examination of a very limited number of speci- 

 mens. His first section contains two species, G. vilis and cyanea, 

 the ^ antennaB of which have the first 15 flagellar joints 

 branched, in the second section the first 12 only. But some 

 species of G. vilis have only the first 14, whilst some of G. hella 

 have the first 15 branched. However the ^ antennae of G. vilis 

 (possibly also of G. cyanea) certainly difier from those of all others 

 in the direction of the first three branches ; the (J forceps also 

 exhibits a considerable diff'erence. 



The thorax is large ; collare moderately developed. Legs 

 tolerably strong, more particularly the hind pair ; tibiae spurred ; 

 empodia distinct ; ungues smooth. Abdomen broader in 9 than, 

 the (J ; the last two or three segments in ^ usually somewhat 

 broader than the preceding, the forceps usually narrowed; the 

 abdomen in ^ of G. vilis and G. Jiavi2)ennis is comparatively 

 longer and more cylindrical than in the other species j the second 

 to fifth or sixth segments are narrowed in G. melanopyga and G. 

 himaculata ; base of abdomen only slightly narrower in G. hella and 

 G. viridis. The male forceps (PI. xxiv., figs. 65-70) consists of 

 a pair of short, fleshy, basal pieces armed usually with a single 

 claw shaped horny appendage ; in G. melanopyga this appendage 

 difi"ers from the others in being more blunt and tridentate at the 

 extremity \ whilst the forceps of G. vilis departs considerably from 

 the common type in being armed with three claw-shaped append- 

 ages, one of which is a fixture and another minutely bidentate at 

 the end The visible appendages of the internal apparatus are 

 variable. I have seen what I take to be the membranous opercule 

 mentioned by Macquart (Dipt. Exot. I. p. 43) in only one species, 



