Genus Hydrellia Robineau-Desvoidy

Hydrellia Robineau-Desvoidy 1830: 790. Type species: Hydrellia communis Robineau-Desvoidy 1830 (= Notiphila griseola Fallén), subsequent designation, Duponchel in d'Orbigny 1845: 743. Cresson 1947: 37 –39 (review, Neotropical species). Wirth 1968: 13 (Neotropical catalog). Zatwarnicki 1988 (world catalog). Mathis & Zatwarnicki 1995: 61 –96 (world catalog). Deonier 1998: 1 –354 (revision of North American species).

Diagnosis. Hydrellia is distinguished from other genera of Hydrelliini by the following combination of characters: body frequently microtomentose, especially face. Head: ocellar setae smaller than pseudopostocellar setae; frontoorbital setae 2, anterior seta proclinate, posterior seta reclinate to lateroreclinate, sometimes with a third, much smaller proclinate seta. Eye bearing numerous interfacetal setulae. Face planate to shallowly carinate. Thorax: dorsocentral setae 2–3 (0+2, 1+2); acrostichal setulae usually in rows; postsutural supra-alar seta usually short, not longer than posterior notopleural seta; scutellar setae 3, middle pair much shorter; notopleural setae 2, these inserted at more or less the same level. Wings: hyaline; costa extended to vein M. Midtibia lacking dorsal, spinelike setae. Abdomen: dorsum comprising tergites 1–5, with tergites 1–2 somewhat fused; sternite 1 greatly reduced or lacking, 2–5 present; male 5th sternite variable in shape but usually U-shaped with posteriorly extended lobes from lateral arms modified and called “copulobi” (Deonier 1998: 15).