During an examination of the Hydromedusae from the Netherlands and adjacent waters present in the collections of the Rijksmuseum van Natuurlijke Historie at Leiden, the Zoological Museum at Amsterdam, and the Zoological Station at Den Helder, some specimens of a medusa were found that proved to belong to Ostroumovia inkermanica (PALTSCHIKOWA-OSTROUMOWA, 1925), a species not previously reported from the region. As the collections, mentioned above, did not contain specimens indentified with this name, some of the medusae were sent to Dr. P. L. KRAMP, Zoological Museum, Copenhagen, who kindly examined them and confirmed the identification.