2 literature references for Hygrotus inaequalis inaequalis (Fabricius, 1777):

Author: Nilsson, Anders N.
Year: 2001
Title:
Source: World Catalogue of Insects, volume 3: Dytiscidae (Coleoptera)
Author: Nilsson, A. N.
Year: 2010
Title:
Source: database. A World Catalogue of the Family Dytiscidae