Latreille, P.A., Lepeletier, A.L.M., Serville, J.G.A., and F.E. Guerin Meneville. 1828. Entomologie, ou histoire naturelle des crustaces, des crachnides et des insectes. Societe de Gens de Lettres, de Savans et dArtistes: Encyclopedie methodique [q.v.]. Histoire naturelle. Paris, 10 (2): 345-833.
Three subgenera of Helius are known from the Oriental Region (Eurhamphidia, Helius, and Rhampholimnobia). They are grouped based on the possession of a rostrom whose length is greater that that of the remaining head and may exceed nearly 5 times its length. The elongate rostrum seen in Helius is similar to that of both Elephantomyia and Toxorhina, but is separated from the former by a lack of tibial spurs and by the singular setae of the legs from the latter (bifid in Toxorhina).
Helius (Helius) is separated from the other subgenera of Helius by the placement of crossveins R-M after the split of Rs, its placement before the spit in both H. (Eurhamphidia) and H. (Rhampholimnobia).
Head: Anterior vertex suppressed, present as a thin strip between the eyes. Rostrum equal to or more commonly longer than head, not exceeding legth of head and thorax combined. Maxillary palpus less than or subequal to the head without rostrum; basal palpomeres subequal, ultimate palpomere may be longer than preceding segments. Antennae: 16 articles; antenomeres variable, suboval or cylindrical.
Wings: Subhylane, commonly patterned with clouds of brown located along veins; cells without microtrichia; wing base not narrowed at wing base, anal angle of wing present. Wing venation: Sc short, Sc2 not removed from Sc1, both elements ending between origin and split of Rs; Sc1 occasionally not attaining wing margin; R1 straight to wing margin; R2 absent; two branches of Rs (R4, R5) attaining wing margin; r-m crossvein after split of Rs; two Medial veins (M1+2, M3) attaining wing margin; cell dm present, rarely absent; CuA crossvein near the split of M; two Cubital veins (CuA1, CuA2) attaining wing margin; two Anal veins (A1, A2) attaining wing margin.
Male hypopygium: 9th tergite (9t) and sternite (9s) fused to a continuous ring. Mesoventral lobe of gonocoxite present, uncommonly reduced. Gonostylus bifid; dorsal gonostyle a simple sclerotized rod, tip variously produced from a simple tip to two to three spines; ventral gonostyle bulbous based with a narrowed slender apex. Aedeagus variable, with one or two terminal openings. Proctriger simple, without modification.
Helius (Helius) is a widespread genus found in all biogeographic regions except Antactica and showing a strong equatorial distribution. The genus finds its highest richness in the Oriental Region (69 species) and is strongly represented in the Neotropical (48 species), Afrotropical (23 species), Australian/Oceanic (15 species), and Eastern Palearctic (17 species) Regions. It is weakly present in both the Western Palearctic (5 species) and Nearctic (2 species) regions.
Throughout the Oriental region the subgenus is widespread and is commonly encountered around flowing waters and waterfalls.
The larval habitats of H. (Helius) are known to inhabit detritus in wet woodlands, marshes, or splash zones.
