The ubiquitous ostracode Darwinula stevensoni (Brady and Robertson, 1870), redescription of the species and lectotype designation.

Darwinula stevensoni (Brady and Robertson 1870) is the type species of Darwinula, the ubiquitous living and fossil nonmarine nominate genus of the Darwinulidae and the Darwinulacea. To date, the additional families Darwinuloididae (fossil), Microdarwinulidae (living and fossil), Panxianidae (fossil), and Suchonellidae (fossil) have been referred to the Darwinulacea. A type specimen for D. stevensoni has not been previously designated. In order to stabilize the species, a lectotype is selected from the type series in the Brady collection at The Hancock Museum, Newcastle upon Tyne. The species is redescribed and reillustrated based on the study of the carapace of a paralectotype and also of valves and appendages of specimens from both England and the United States. Living species of Darwinula have a cosmopolitan distribution in fresh and brackish water. Fossil Darwinulacea, documented in the Carboniferous, serve as indicators of continental Paleozoic to Holocene deposits. - Author