340 



Leech and Chandler: Coleoptera 



in Paracymus; pleural lobes usually prominent; abdomen 

 not noticeably truncate 5 



— Ocular areas round, closely aggregated; legs absent; 

 pleural lobes not prominent; abdomen truncate; ligula 

 exceeding palpi and pointed (fig. 13:37d) 



Cercyon Leach 1817 



5. First antennal segment not distinctly longer than 

 following 2 taken together; fingerlike antennal appen- 

 dage present; labro-clypeus with teeth usually well 

 defined; mouth parts stouter; mandibles not grooved 

 internally; stipes large and swollen, usually with an 

 inner row of 5 stout setae; externofrontal angles of 

 mentum not prominent, rounded; legs much shorter, 

 femora without fringes of swimming hairs; gills and 

 prostyles absent 6 



— First segment of antennae distinctly longer than fol- 

 lowing 2 taken together; fingerlike antennal appendage 

 absent; labroclypeus with teeth small or absent; 

 mouth parts more slender; mandibles grooved inter- 

 nally; stipes not swollen, with setae arranged differ- 

 ently; externofrontal angles of mentum prominent and 

 acute; legs very long; femora with fringes of long 

 swimming hairs; gills present (Hydrochara, Tropisternus) 

 or absent (Hydrophilus); prostyle present 12 



6. Frontal sutures parallel and not uniting to form an 

 epicranial suture; left expansion of epistoma much 

 more prominent than the right and with a row of stout 

 setae; ligula absent; reduced sclerites of meso- and 

 metathorax widely separated; tarsi about as long as 

 tibiae (fig. 13:37e) Laccobius Erichson 1837 



— Frontal sutures not parallel, and they may or may 

 not unite to form an epicranial suture; lateral expan- 

 sions of epistoma similar and usually in line with 

 anterior margin of labro-clypeus, ligula present and 

 longer than segment 1 of palpus; sclerites of meso- and 

 metathorax reduced but not so widely separated; tarsi 

 shorter than tibiae 7 



7. Antennae shorter and antennal appendage more promi- 

 nent; epicranial suture absent; legs reduced; abdomen 

 more truncate; cercus with long terminal seta 8 



— Antennae longer and antennal appendage less prominent; 

 epicranial suture present but usually short; legs 



fairly long, not reduced; abdomen narrowed caudally; 

 cercus with a shorter terminal seta 9 



8. Frons truncate behind; labrum tridentate, lateral 

 teeth bifid; mandibles with 2 inner teeth; ligula about 

 as long as palpi, apparently 2-segmented; anterior 

 margin of pronotum without a fringe of stout setae; 

 legs not visible from above (fig. 13:37/) 



, Paracymus Thomson 1867 



— Frons rounded behind; labrum quadridentate; mandibles 

 with 3 inner teeth; ligula not as long as palpi, 1-seg- 

 mented; anterior margin of pronotum with fringe of 

 stout setae; legs barely visible from above (fig. 13:37p) 



Anacaena Thomson 1859 



9. Mandibles asymmetrical, the right with 2 inner teeth, 

 the left with only 1; abdomen with prolegs on segments 

 3-7 (fig. 13:38a) Enochrus Thomson 1859 



— Mandibles symmetrical each with 2 or 3 inner teeth; 

 abdomen without prolegs 10 



10. Labroclypeus with 5 distinct teeth, outer left tooth 

 a little distant from rest; each mandible with 3 inner 

 teeth; mentum wider at base (fig. 13:386) 



Hydrobius Leach 1815 



— Labroclypeus with at least 6 teeth; each mandible 

 with 2 inner teeth; mentum narrower at base 11 



11. Labroclypeus with 6 distinct teeth, placed in 2 groups, 

 2 on left and 4 on right; mentum covered with small 

 spines; anterior sclerites of metathorax with caudal 

 projections (fig. 13:38c) .... Helochares Mulsant 1844 



— Labroclypeus with more than 6 teeth, those toward 

 right not clearly defined and with several smaller 

 teeth; mentum with small spines only toward base; 

 anterior sclerites of metathorax without caudal pro- 

 jections, rectangular (fig. 13:38d) 



Cymbiodyta Bedel 1881 



12. Head subspherical; labroclypeus without teeth; each 

 mandible with a single inner tooth; ligula not longer 

 than 1st segment of palp; gills absent; pronotum not 

 entirely chitinized (fig. 13:38e) 



' Hydrophilus Geoffroy 1762 



— Head subquadr angular, narrowed behind; labroclypeus 

 with inconspicuous teeth; each mandible with more 

 than 1, usually with 2 inner teeth; ligula distinctly 



Fig. 13:38. Hydrophilidae, larvae, a, Enochrus sp.; b, Hydrobius fusipes; c, Helochares 

 maculicollis; d, Cymbiodyta sp.; e, Hydrophilus friangularis; f, Tropisternus sp.; g, Hydrochara 

 sp. (a,c-g, Richmond, b, Boving and Henriksen, 1938). 



