Chasmogenus Sharp, 1882

Glynn, Rachel D. & Short, Andrew Edward Z., 2021, New species and records of Chasmogenus Sharp, 1882 from the southwestern margin of the Guiana Shield (Coleoptera: Hydrophilidae: Acidocerinae), Zootaxa 5048 (3), pp. 435-443 : 442-443

Key to the species of Chasmogenus Sharp of Venezuela, Suriname, Guyana, French Guiana, and Brazil north of the Amazon River

We have modified the key presented in Smith & Short (2020) to insert the three species described here. All three species would key to couplet 13 in the original key, so we have not repeated those here. We emphasize that examination of the genitalia is crucial to accurate identifications and unassociated females of the three species described here cannot be identified with precision.

13 Aedeagus with apex of median lobe long, distinctly extending beyond the apex of the parameres; basal piece short, one-third the total length of the parameres or less (e.g. Smith & Short 2020: fig. 15A–E, 15G–I)............................. 14

- Aedeagus with apex of median lobe shorter or not extending beyond the apex of the parameres; basal piece long, up to one-half the length of the entire aedeagus........................................................................ 17

14 Parameres of aedeagus smooth along outer edges, not sinuate or undulate, apex of median lobe acuminates at the apex ( Smith & Short 2020: fig. 15H, I); gonopore situated toward the apex of the median lobe............ C. acuminatus Smith & Short

- Parameres moderately sinuate along outer margins; gonopore situated about in the middle of the median lobe............15

15 Median lobe of aedeagus terminating in a broadly rounded apex past the apex of the parameres (e.g. Smith & Short 2020: fig. 15E);.......................................................................... C. ligulatus Smith & Short

- Median lobe narrowing to a moderately to acutely pointed apex past the apex of the parameres...................... 16a

16a Median lobe with apex acuminate (e.g. Smith & Short 2020: fig. 15A–D); emargination of the clypeus narrow (e.g. Smith & Short 2020: figs 5D–F, 10D).......................................................................... 16b

- Median lobe with apex rounded ( Smith & Short 2020: fig. 15G); dorsal coloration dark brown, emargination of the clypeus rounded to angulate............................................................. C. undulatus Smith & Short

16b Outer margins of parameres with two constrictions (bisinuate) (e.g. Smith and Short 2020: fig. 15A–D); dorsal coloration dark reddish brown and translucent (e.g. Smith and Short 2020: figs. 5D–F, 10D)................... C. pandus Smith & Short

- Outer margins of parameres with a single constriction (sinuate) (fig. 4A–D); dorsal coloration uniformly dark brown (fig. 2A, B).................................................................................... C. clinatus sp. n.

17 Median lobe of aedeagus shorter than length of parameres, aedeagus symmetrical................................. 18

- Apex of median lobe of aedeagus approximately even with apex of parameres.................................... 19

18 Apex of parameres bluntly squared ( Smith & Short 2020: fig. 14F).......................... C. schmits Smith & Short

- Apex of parameres rounded ( Smith & Short 2020: fig. 14G, H).......................... C. guianensis Smith & Short

19 Distinct dark patches on mesal portion of clypeus and labrum ( Smith & Short 2020: fig.10A).................................................................................................. C. brownsbergensis Smith & Short

- Clypeus and labrum without distinct dark patches........................................................... 20

20 Aedeagus with parameres straight along outer margins, only curving inward past the position of the gonopore........... 21

- Aedeagus with parameres that curve slightly inward along the outer margins throughout the entire length (figs. 5A, B)............................................................................................... C. inpa sp. n.

21 Apex of median lobe rounded triangular in shape (figs. 5C, D).................................... C. gironae sp. n.

- Apex of median lobe acutely triangular in shape............................................................ 22

22 Total body size ≤ 3.8 mm, dorsal coloration very dark brown................................. .. C. gato Smith & Short

- Total body length ≥ 3.8 mm, dorsal coloration pale orange-brown..................... C. clavijoi Smith & Short (in part)