42 R. W. CROSSKEY 



plesiomorphic form known among the imitomyiines, with the various described 

 species of Imitomyia (and its synonym Diplopota) representing apomorphic deriva- 

 tives from a Riedelia-hke ancestor in which there has been enormous elongation 

 of the proboscis (including the labellae), reduction in the abdominal vestiture and 

 reduction of the aristal plumosity. Proriedelia is intermediate, showing the closure 

 of cell R 5 found in Imitomyia but retaining the short proboscis of Riedelia. 



The main characteristics of the Imitomyiini are as follows. Head with eyes very strongly 

 approximated, almost holoptic in both sexes; upper frons almost obliterated and with the 

 parafrontals meeting or virtually so in the mid line; upper eye facets usually conspicuously 

 enlarged in the female in comparison to the lowermost facets. Eyes bare. Facial carina 

 present (Text-fig. 31), very strong, of characteristic shape, widening ventrally and flattened 

 anteriorly, bowed in profile and with the sides strongly pinched in so that the antennae lie 

 in deeply excavate foveae. Antennal axis about level with eye middle, head about as long 

 or slightly longer at epistomal axis than at antennal axis. Head chaetotaxy very reduced, 

 inner and outer vertical setae and orbital setae absent in both sexes. Frontal setae reduced, 

 almost hair-like except for lowermost pairs, frontal rows reaching to level of antennal insertions. 

 Facial ridges bare, parafacials bare or haired. Vibrissae weak or moderate, about level with 

 or slightly below epistomal margin, epistome warped forwards and separated from facial carina 

 by a distinct depression when seen in profile. Gena at least as wide as length of third antennal 

 segment. Ocellar triangle prominent, ocellar setae weak or absent. Upper occiput concave, 

 postorbits virtually absent (the rows of postocular setae more or less abutting the eye margins), 

 occipital vestiture dark. Antennae short or very short, third segment evenly rounded apically ; 

 arista thickened only at the base, segments not elongate, pubescent or thickly plumose. Palpi 

 filiform, either subequal in length to antenna or not longer than third antennal segment. Pro- 

 boscis very slender, either short and stiff and about as long as eye-height or conspicuously 

 elongate, sometimes geniculate, proboscis including labellae sometimes so attenuate as to 

 exceed whole body length. Thoracic chaetotaxy weak or very weak. Humeral callus with two 

 or three setae, if three then standing in line. Usually one ph seta. One or two post ia setae. 

 dc setae varied, from o + 1 to 2 -f- 3. acr setae varied, usually undifferentiated presuturally, 

 at least one (prescutellar) pair and sometimes more postsuturally. pra seta absent, second 

 sa seta absent or (in Riedelia) present but very small. Prosternum and propleuron bare 

 (an adventitious hair present on one side of the prosternum in P. petiolata holotype). Propleural 

 and prostigmatic setae very weak or moderate. Two stpl setae (1 + 1). Pteropleural seta 

 moderately well developed [Riedelia), very weak or absent, pteropleuron sometimes wholly 

 bare. Hypopleural setae reduced. Infrasquamal setulae present or absent. Posteroventral 

 declivity of the thorax membranous medially. Fore coxa bare on the inner anterior surface. 

 Scutellum with two pairs of marginal setae (basals and very strong crossed apicals). Legs with 

 very weak setae, these often reduced to mere hairs, but mid tibia usually with at least one 

 ad and a v seta differentiated. Wings narrow, hyaline or nearly so, veins totally bare. Cell 

 i? 5 narrowly open at wing margin (Riedelia) or with a very long petiole that is as long as or 

 longer than m-cu and ends exactly in the wing apex. Bend of vein M abruptly rounded or 

 sharply angulate (sometimes with trace of M 2 appendix). Cross-vein m-cu meeting vein M 

 about midway between r-m and the bend or slightly closer to either. Second costal sector 

 very short, bare ventrally. Lower calyptrae widely divergent from scutellum, forming promi- 

 nent round lobes. Abdomen with Ti + 2 not excavate to its hind margin. Abdominal 

 vestiture very weak or entirely hair-like, rows of long fine marginals sometimes differentiated 

 on each tergite. Sternites largely exposed. Female terminalia as described in detail by 

 Townsend (1936a : 76) and figured by Bezzi (1917), characterized by a pair of large strongly 

 sclerotized shining black dorsolateral pliers-like lamellae that usually bear strong recurved 

 spines or hooks. [Length 2-6 mm, the tribe including the smallest known Tachinidae (speci- 

 mens of Imitomyia nitida Emden and Himantostomopsis hungarica Thalhammer sometimes 

 not exceeding a length of 2-0 mm).] 



