Pseudagrion microcephalum (Rambur, 1842)-sifting through a putative familiar species, with erection of two new species (Odonata: Coenagrionidae).

Specimens of the Pseudagrion blue-group allied to P. microcephalum (Rambur, 1842) were studied with special attention to the male caudal appendages and genital ligulae. The males of P. microcephalum are morphologically re-characterised, and the species is considered to have a limited range that includes India, Pakistan, Nepal, Bangladesh, and Sri Lanka. The status of P. siamense Fraser, 1922 is revised and considered a distinct species, with the scientific name removed from synonymity and a neotype designated and described (♂, 7.viii.1972, stream at Ang Kep Nam-Bang Phra environments, South Chon Buri, Thailand, approximately 13.205°N, 100.975°E, G. von Rosen leg., GvRosen no. 1753; deposited at the Zoological State Collection Munich, Germany). Two new species are erected and figured: P. crenatumsp. nov. from Australia (holotype ♂, 2.x.1915, Caboolture, Queensland, Australia, approximately -27.084°N, 152.951°E, R.J. Tillyard leg., no. 14110; deposited at the Forschungsinstitut und Naturmuseum Senckenberg, Frankfurt am Main, Germany); and P. piratasp. nov. from the Philippine Islands (holotype ♂, 17.i.1992, Barili, Montayupan falls, Cebu Island, Philippines, approximately 10.101°N, 123.535°E, Th. Borromeo Jr. leg., ex. Coll. Roland A. Müller, no. 975694; deposited at the Naturalis Biodiversity Centre Leiden, the Netherlands). The range of P. coarctatum Lieftinck, 1932, a species previously known only from a few records at Jayapura and Sentani Lake in northeastern Indonesian West Papua, is extended to Sulawesi, the Moluccas and the Solomon Islands; the male is morphologically re-characterised and illustrated, and the female described. Photographs of the holotypes of P. microcephalum, P. coarctatum and P. starreanum Lieftinck, 1949 are provided. In addition, P. stainbergerorum Marinov, 2012 stat. nov. is proposed, based on distinct morphological differences from P. microcephalum. A key to males of the Pseudagrion blue-group is provided, including illustrations of the male caudal appendages and partly of the genital ligulae for all species treated. Pseudagrion daponshanensis Zhou & Zhou, 2007 is transferred to the genus Coenagrion.