On the taxonomy of water mites (Acari: Hydrachnidia) described from the Palaearctic, part 1: Hydrachnidae, Limnocharidae and Eylaidae Author Davids, Kees Author Sabatino, Antonio Di Author Gerecke, Reinhard Author Gledhill, Terence Author Smit, Harry text Zootaxa 2005 1061 36 64 journal article 10.5281/zenodo.170186 d91ae7dd-a600-4f24-a890-7201060d61b6 1175­5326 170186 Hydrachna williamsoni Soar, 1908 Species incerta Material examined: Female, NHML , C.F.G. "Dr. C. F. George coll. 1925 VI 24 144". "Lincolnshire Dr.C.F.George Coll. 1925 VI 24. 144. Balsam, 1904". Location of holotype unclear. Discussion: The only specimen known in European collections is obviously a juvenile. From many points of view it is similar to H. processifera (frontal area with poorly developed, roundish sclerite dots near postocularia, general shape of genital field, with L/ W 400/700, Cx­4 with a hook­like extension directed laterally). The transverse position of the gnathosoma and its appendages does not allow for measurements. As proposed by Gledhill & K.O. Viets (1976) , this species should be considered a species incerta and not listed in faunistic inventories.