Cydistomyia, Taylor, 1919

Mackerras, I. M., Spratt, D. M. & Yeates, D. K., 2008, Revision of the horse fly genera Lissimas and Cydistomyia (Diptera: Tabanidae: Diachlorini) of Australia, Zootaxa 1886 (1), pp. 1-80 : 11-12

Genus CYDISTOMYIA Taylor

Cydistomyia Taylor, 1919: 47 ; Oldroyd 1949: 342; Mackerras 1959: 166; 1971 b: 419; Daniels 1989; 285; Trojan 1998: 69; Bickel & Elliot, 1998 -2005: 2. Type species. Cydistomyia doddi Taylor (= C. albithorax Ricardo ), by monotypy [New Guinea; wrongly recorded as Kuranda, north Qld)].

Chasmia Enderlein, 1922: 344, 1925: 331 ; Oldroyd 1949: 333; Mackerras 1962 b: 105 (as subgenus of Cydistomyia ); Mackerras 1971 b: 412 (restored as genus); Daniels 1989: 285; Trojan 1998: 20. Type species. Chasmia bicincta Enderlein (= C. basifasciata de Meijere ), by monotypy [New Guinea].

Chasmiella Enderlein, 1922: 344, 1925: 331 ; Oldroyd 1949: 333; Mackerras 1962: 107 (as synonym of Chasmia ); Mackerras 1971 b: 414 (as one of two subclones, Chasmia , sensu stricto and ” Chasmiella ”); Trojan, 1998: 69 (removal from synonymy with Chasmia ). Type species. Tabanus breviusculus Walker , by monotypy [New Guinea].

Diagnosis. Very small to large, usually of medium build, but sometimes slender or rotund; body smooth, nonmetallic (except C. casuarinae , C. cyanea ), sometimes rather bare; body length 6–21 mm.

Female. Eyes bare (except C. casuarinae , C. improcerus , C. pruina , C. victoriensis ), unbanded (except musgravii , rivularis , atmophora ). Frons mostly or entirely tomentose, slightly convergent to slightly divergent, index greater than 3 (except C. heydoni [Papuan], C. griseicolor ); callus usually well developed (absent or rudimentary in three Papuan species); subcallus tomentose (except in two Papuan species); parafacials tomentose; face usually tomentose, occasionally more or less shiny; antennae sometimes slender, scape at most slightly swollen; palpi usually slender. Thorax and legs undistinguished. Wings sometimes long, sometimes diffusely darkened, but almost entirely blackish in C., kamialiensis and C. imitans [Papuan] (cf. Goodwin 1999); R 4 usually without appendix (rudimentary in some: C. torresi and C. brevior ). Terminal abdominal segments usually dorsoventrally compressed, occasionally modified ( C. lamellata group [Papuan]).

Male. Sexual dimorphism slight to moderate. Eyes usually bare (except C. casuarinae , C. palmensis , C. bancroftae , C. improcerus , C. victoriensis , C. musgravii , C. rivularis ), upper facets usually enlarged and contrasting with lower; ocellar tubercle sometimes small and hidden, usually visible at vertex; palpi conical or acorn-shaped. Terminalia undistinguished.

It is difficult to frame a satisfactory definition of this genus, because it is characterised essentially by lack of specialisation. Moreover, the incipient specialisations that do occur introduce numerous exceptions into what could otherwise be simple statements. The general features of the type species, including its rather broad build and unusual thoracic pattern, represents a divergent branch rather than the central core of the genus. The Australian species are less diverse than the Papuan species, suggesting that they have been subjected to less intense selection pressures. An appendix on R 4 is common in Papuan species.