Morphometric differences between morphotypes and effect of body size on Elytral Index (EI) of Hydrobius. EI = length of the elytra / maximum width of elytra. 113 specimens measured. Independently fitted lines for each morphotype are shown, slopes not significantly different. Type specimens and specimens of H. f. subrotundus and H. f. fuscipes collected in sympatry (Rinn = locality Rinnleiret (Norway), Mot = Motzen (Germany) and Ola = Öland (Sweden)) are labeled.