Hydrachna cruenta Müller, 1776

Hydrachna schneideri Koenike, 1895: synonymy first proposed by K. Viets (1935) ­ here confirmed.

Material examined: Hydrachna cruenta male SMNH 6043, Östergötland, Källstad socken 13.6.1913 Lundblad; female SMNH 752 Södermanland, Björnhuda, 5.7.1923 Lundblad; Hydrachna schneideri lectotype male, SMNH 375 Heiligenrode, 2370 Ostfriesland.

Discussion: Notwithstanding the lack of type material of H. cruenta, it is generally accepted that the male syntype of H. schneideri Koenike, 1895 is identical to that species. As this specimen must be considered the lectotype of H. schneideri, this name is obviously unavailable in taxonomic nomenclature and the valid name for all specimens published under the name of H. schneideri is H. skorikowi (Piersig, 1900) (see under this name for a detailed discussion).