Armostus, Sharp, 1890

Hoshina, Hideto & Satô, Masataka, 2006, A Taxonomic Study of the Genus Armostus (Coleoptera: Hydrophilidae) from Japan, The Coleopterists Bulletin 60 (2), pp. 95-104 : 96

Key to the Japanese Species of the Genus Armostus

1 Dorsum usually black or dark brown, rarely brown; elytra with a bright yellowish brown patch in the apical part ( Figs. 6–8); prosternum provided with a relatively low carina whose ventral margin is almost straight in lateral view ( Figs. 14 and 15); metaventrite provided with easily visible lateral sutures running near episternum and arranging in triangles with lateral margins metaventrite ( Figs. 18 and 19). ..................................................................................................... 2

1 9 Dorsum usually brown; basal 2/3 of elytra brown and apical 1/3 light brown ( Figs. 9–11), with a black patch ( Figs. 9 and 10) or rarely concolorous ( Fig. 12); prosternum provided with a relatively high carina whose ventral margin is weakly curved in lateral view ( Figs. 16 and 17); lateral sutures of metaventrite hardly visible ( Figs. 20 and 22). .................................................................... 3

2(1) Punctures of head relatively small ( Fig. 2); pronotum very sparsely pubescent ( Fig. 2); all punctures of pronotum almost of the same size ( Fig. 2); elytra widest approximately 1/3 at base; pale spot of elytra wide ( Figs. 6 and 7); prosternum provided with a very low carina ( Fig. 14); median lobe of aedeagus almost straight at apex in ventral view ( Fig. 26). ........................................................ ............................................................ Armostus schenklingi (d’ Orchymont)

2 9 Punctures of head relatively large ( Fig. 3); pronotum relatively densely pubescent ( Fig. 3); punctures of pronotum composed of small and large punctures ( Fig. 3); elytra widest approximately 1/7 at base; pale spot of elytra ( Fig. 8); median lobe of aedeagus pointed apically in ventral view ( Fig. 28). ............... ................................................................................ A. nigricans , new species

3(1 9) Body length 1.7–2.0 mm, usually less than 2 mm; elytra almost as long as wide, and in sometimes specimens with a clear black patch on central area ( Figs. 9 and 10); prosternum provided with a relatively high carina ( Fig. 16); preepisternal elevation of mesothorax about 3.0 times as long as wide ( Fig. 20). ................ .............................................................................. A. crenulatus (Régimbart)

3 9 Body length 2.0– 2.3 mm; elytra slightly longer than wide ( Fig. 12); preepisternal elevation of mesothorax about 2.1 times as long as wide ( Fig. 22). ................ ......................................................................... A. ohyamatensis , new species