Genus Hydrophilus subgenus Dibolocelus

→ 2Wide shape [Abb. 1], generally black color, with greenish, non-metallic reflections.

→ 4-Narrower shape, tarsi II, in both sexes, approximately 1.5 times the tibia. ♂: labial palp not triangular; anterior tibial spurs like figuras 2 and 5. ♀: femurs II with dense stippling.

masculinus Régimbart♂: Maxillar palpes [Abb. 2]. 2nd part of the labial palp expanded in a triangle [Abb. 3]; tarsi II disproportionately long (twice as the tibia); genitalia as [Abb. 4]; tarsus I and tibial spurs as [Abb. 5]. ♀: labial palp as [Abb. 3]; 2nd article 4/5 of the 1st; femurs II with sparse stippling. South America.

→ 3-Palpes different. Central and North America

ovatus Gemminger & Harold, 1868Maxillary palpes of males modified with third segment flattend and widened. Protarsal claws of ♂ enlarged but subequal in size and shape. Fifth protarsal segment slightly widened in ♂. Eastern United States. eastern coast of Mexico, and extreme southeastern Canada. 30-35 mm. This species is not mentioned for Mexico by Arce-Pérez & Moron (l.c.)

purpurascens Régimbart, 1901-Habitus [Abb. 1]. Maxillary palps of ♂ with second and third inflated segments (globose); the third deeply excavated ventrally; abdomen with ventrite 4 raised on the center as a thick, glabrous keel, the fifth sharply raised and with a broad subtriangular glabrous area; the keel of 4th ventrite projects slightly over 5th. Aedoeagus [Abb. 6]. Overall length 35-38mm.

iricolor RégimbartShape pointed behind, generally green color with iridescent reflections (sometimes almost black). ♂: Tarsus I [Abb. 7]. Maxillar palpes [Abb. 8]. 2nd labial palp joint clubbed [Abb. 9]; last segment of maxillary palp approximately 4/5 of the previous one, the latter little less than the 2nd; genitalia as [Abb. 10]. ♀: 2nd labial palp segment obliquely truncated [Abb. 9], 3rd segment 2/3 of the 2nd.

palpalis (Brullé)-Shape less sharp behind, color generally black, sometimes with greenish, non-metallic reflections. ♂: Tarsus I [Abb. 11]. Maxillar palpes [Abb. 12]. 2nd subparallel labial palp segment [Abb. 13]; last segment of maxillary palp a little more than half of the penultimate, the latter clearly smaller than the 2nd; genitalia as [Abb. 14]. ♀: 2nd subparallel labial palp joint [Abb. 13], 3rd segment 4/5 of the 2nd.