BY FREDERICK A. A. SKUSE. 55 



enable us to form any adequate opinion from whence they 

 originated, or in which direction they travelled, though we may 

 have some vague notion how they have become dispersed. It is 

 obviously highly improbable that these small frail Hies could have 

 migrated across the wide tracts of water now separating certain 

 countries, but became distributed at some period during which 

 these watery Imrriers dividing or completely isolating land at the 

 present day, did not exist. If we consider the changes this 

 earth's surface has undergone, and remember that in the Triassic 

 period for instance the island-continent of Australia was part of 

 the Palsearctic or Asiatic mainland, and that at that time the land 

 was not broken up into the islands of the Eastern Archipelago, 

 thus affording an opportunity for migration, some little light may 

 be thrown on this interesting subject, which, however, cannot 

 be further pui'sued in the present paper. 



V. Imago. 



External structure. 



The head is small, above broader than long, round when viewed 

 from the front. Eyes generally lunate or reniform, more or less 

 contiguous on the front. Ocelli wanting in the sub-family Ceci- 

 DOMYiNA, but extant in the Lertre.mina. Proboscis shoi-t, thick, 

 fleshy, directed towards the pectus. Palpi prominent, four-jointed, 

 the first joint short, the last usually longest. Antennae long, 

 nioniliform or cylindrical, generally \'erticillate-pilose, seldom 

 without vei-ticils, 10- to 36-jointed, of which the two basal joints 

 are more or less cupuliform ; flagellar joints sometimes pedicelled 

 in the ^ and sessile in the 9 ; sometimes of the same structure, 

 pedicelled or sessile, in both sexes. The thorax roundish, in some 

 8peci(,'S giljbose, sometimes extending over the head iu the form of 

 a hood ; without a transverse suture. Halteres never completely 

 bare, often considerably haii'ed or scaled ; the stalk long mid 

 slender ; club large. Legs generally very long and siendei-. 

 C0X88 short ; femora not thickened ; tibiso without spurs ; tarsi 

 five-joint*id ; tlie metatarsal joint much shortened iu tim flrst 



