Hydrophilus (Dibolocelus), 1891

Arce-Pérez, Roberto, Arriaga-Varela, Emmanuel, Novelo-Gutiérrez, Rodolfo & Navarrete-Heredia, José L., 2021, Giant water scavenger beetles Hydrophilus subgenus Dibolocelus (Coleoptera Hydrophilidae) from Mexico with description of two new species, Zootaxa 5027 (3), pp. 387-407 : 405

Key for the species of Hydrophilus (Dibolocelus) from Mexico and Central America

Note. The first characters to appear in the couplets are those shared by both sexes when available. However, the best characters for specific identification are those found in male specimens. We recommend following this key with caution if only female specimens that are not associated to males are available.

1. Sixth antennomere long and oval, yellowish brown, almost completely covering the first article of antennal club ( Figs. 23, 33); abdominal ventrites with vestiture leaving a slender oval glabrous area at mid-line in ventrite 4 and broader sub-triangular one in ventrite 5 ( Figs. 31, 35) in both sexes. Males with robust (inflated) maxillary palpi, third palpomere with a deep broad ventral excavation ( Figs. 29, 33), females with narrow palpi, without ventral excavation................................... 2

1’ Sixth antennomere short and oval, dark brown, not covering the first article of antennal club ( Figs. 7, 11, |5, 25); abdominal ventrites with vestiture leaving a wide oval glabrous area at mid-line in ventrites 3–4; and a broader sub-rectangular one in ventrite 5 in both sexes ( Figs. 2, 4, 6); males with maxillary palpi narrow ( Fig. 25) or slightly flattened towards apex ( Figs. 7, 11, 15) in both sexes.................................................................................. 3

2 (1). Anterior margin of mentum truncated and straight in both sexes ( Fig. 33); male genitalia with broad parameres, slightly directed outward, with broad subtriangular apex ( Fig. 36 a, b)........................... H. (D.) cf. purpurascens Régimbart

2’ Anterior margin of mentum rounded, unknown female ( Fig. 29); male genitalia with parameres comparatively narrow, markedly directed inwards, with slender round apex. ( Fig. 32 a, b)................................. H. (D.) pollens Sharp

3 (1’). 3 (1’). Male with maxillary palpomeres 2 and 3 distinctly flattened and wide towards apex ( Figs. 7, 11), slightly flattened in female; male with anterior tibiae internal spur sub-rectangular and with apex truncate ( Figs. 8, 12), sub-triangular and acute in female.............................................................................................. 4

3’ Male and female with maxillary palpomeres 2 and 3 distinctly slender, only slightly flattened ( Figs. 15, 25); males with anterior tibiae internal spur sub-rectangular with apex truncate straight ( Fig. 16) or markedly bifid ( Fig. 26).................... 5

4 (3). Metaventral spine short, not surpassing the posterior 3/4 of second abdominal ventrite ( Figs. 4, 13); third palpomere very wide and flattened with its inner margin slightly curved ( Fig. 11). Males with fifth protarsomere somewhat flattened with a small internal laminar expansion, shorter than previous tarsomeres together ( Fig. 12);............ H. (D.) pseudovatus sp. nov.

4’ Metaventral spine long, surpassing the posterior margin of second abdominal ventrite ( Figs. 2, 9); third palpomere slightly wide and flat, compared to H. (D.) pseudovatus , with its inner margin slightly straight ( Fig. 7). Males with fifth protarsomere subcylindrical, without a laminar expansion, longer than previous tarsomeres together ( Fig. 8).............................................................................................. H. (D.) ovatus Gemminger & Harold

5 (3’) Males with fifth protarsomere as long as the basal together, flat and with evident internal laminar expansion; internal spur of anterior tibiae of males sub-rectangular with apex truncate ( Fig. 16)....................... H. (D.) nucleoensis sp. nov

5’ Males with fifth protarsomere shorter than previous tarsomeres together, wide and without internal expansion; internal spur of anterior tibiae of males with bifid apex ( Fig. 26)............................ H. (D.) violaceonitens Jacquelin du Val