The name Euglesa is not a nomen nudum; being published in 1832 as a junior synonym by Jenyns it was nomenclaturally made available by Leach due to his 1852 publication (see ICZN article 11 (e)). The author of Euglesa is, according to ICZN article 50 (g), Jenyns (1832); so far, most authors considered Leach (1852) as its author. The identity of Euglesa henslowiana Jenyns, 1832, the type species of Euglesa by monotypy, is unknown. The description of the animal by Leach refers clearly to a Musculium or a Sphaerium species. However, these characters cannot be used to unravel the identity of E. henslowiana, as the taxon is based on dry material only, namely the specimens labelled by Leach as E. henslowiana, specimens that were exhibited for a long time in the British Museum (and investigated in that museum by Jenyns). The whereabouts of this lot is unknown. The type locality of E. henslowiana is the river Cam and/or the marshes near Cambridge; it is therefore not a marine species. It is argued that Euglesa is most likley a Pisidium species, but it is unknown to which species henslowiana actually belongs (not amnicum) As such, Euglesa is a nomen dubium. Because we cannot neglect the name Euglesa in any subdivision of Pisidium, because it is the oldest available name, a neotype should be selected to ensure nomenclatural stability. This neotype should preferably be a specimen of Pisidium casertanum.