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Orvasca Walker Gen. rev.

Type species: subnotata Walker.

Synonyms: Chionophasma Butler (type species paradoxa Butler, Australia) syn. n.; Ocybola Turner (type species semifusca Walker, Australia) ?syn. n.

This is a diverse and widespread genus of mostly small species that is again best defined on male genitalic characters. The facies is remarkably variable, including pure white, black and strongly patterned and colourful types. Some species have facies similar to that of Somena species and members of the Nygmia atereta Collenette group (See Nygmia atereta Collenette comb.n). The venation is similar to that in Somena: vein M2 in the hindwing is lost. M2 is present in Ocybola, however, so this synonymy, based on genitalic features, is tentative.

The male genitalia are distinguished primarily by two features: a rugose protrusion (possibly the gnathus) ventral to the uncus; a flap, possibly associated with the juxta, between the saccular bases of the valves that overlaps the saccus. The valves themselves are bifid, often deeply divided, the bifurcations often rather unequal and always more splayed than in Somena, usually strongly so, and the upper one may become inturned. The uncus is typically short, and the aedeagus often has an apical spur.

The female genitalia are variable, but the bursa has a bicornute signum.

The biology of the type species is described below.

The full composition and geographic limits of the genus are still to be resolved, but it will probably prove to include a high proportion of the smaller Australasian species. The most easterly species are O. aliena Butler comb. n. (N. Australia, New Caledonia), O. dolichocera Collenette comb. n. (Vanuatu) and O. dimorphissima Holloway comb. n. (New Caledonia). Other species with the generic male genitalic characters are O. fulvonigra Swinhoe comb. n. and O. lavella Bethune-Baker comb. n. from the Solomons, O. aurantiaca Hampson comb. n. (N. E. Himalaya, Peninsular Malaysia (slide 2585)), and O. irrorata Moore comb. n. (Java: see Somena above for discussion of potential homonymy).

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