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Brown, H.P. (1972). Aquatic dryopoid beetles (Coleoptera) of the United States. Biota of Freshwater Ecosystems: Identification Manual, no. 6. Water Pollution Control Research Series, EPA, Washington, D.C. ix + 82 pp.

An illustrated key is given for all known species of adult dryopoid beetles of the United States which have aquatic stages and might be useful as indicators of water quality. A key is also given to the genera of larvae.

For each species the known habitat and range are given. Life histories are briefly outlined and methods for collection, preservation, storage and identification are suggested.

Two new species, Optioservus ozarkensis Collier and Optioservus sandersoni Collier, are described.

The family and genera included in the keys are:

Chelonariidae--Chelonarium
Elmidae--Tribe Larini: Lara, Phanocerus; Tribe Elmini: Ampumixis, Ancyronyx, Atractelmis, Cleptelmis, Cylloepus, Dubiraphia, Elsianus, Gonielmis, Heterelmis, Heterlimnius, Hexacylloepus, Macronychus, Microcylloepus, Narpus, Neocylloepus, Neoelmis, Optioservus, Ordobrevia, Oulimnius, Promoresia, Rhizelmis, Stenelmis, Zaitzevia
Dryopidae--Dryops, Helichus, Pelonomus
Limnichidae--Limnichinae: Limnichus, Lutrochus, Physemus
Cephalobyrrhinae--Throscinus
Psephenidae--Eubriinae: Acneus, Dicranopselaphus, Ectopria; Eubrianacinae: Eubrianax; Psepheninae: Psephenus
Ptilodactylidae--Anchycteis, Anchytarsus, Stenocolus.
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