Fig. 13:39. Hydrophil idae, pupae, a, Hydrophilus triangularis; 

 b, Tropisternus lateralis; c, Berosus sp.; d, Cercyon analis (o-c, 

 Wilson, 1923; d, Bi'ving and Henriksen, 1938). 



longer than 1st palpal segment; pronotum entirely 

 chitinized; gills present but more or less rudimentary 

 13 



13. Mentum with sides nearly straight; frontoexternal 

 angles very prominent; pleural gills rudimentary but 

 indicated by tubercular projections, each with several 

 terminal setae (fig. 13:38/) ... Tropisternus Solier 1834 



— Mentum convex towards basal half; frontoexternal 

 angles less prominent; pleural gills fairly well devel- 

 oped and pubescent (fig. 13:38<7) 



Hydrochara Berthold 1827 



Key to Certain Genera of Nearctic Hydrophl lldoe 

 Pupae 



The pupae of many genera of Hydrophilidae are 

 unknown. 



The following key is adapted from one given by 

 Boving and Henriksen (1938), with Tropisternus 

 interpolated from the short key in Wilson (1923). A 

 somewhat different key to most of the same genera 



341 



Leech and Chandler: Coleoptera 



is given by Richmond (1920). It should be noted 

 that because of taxonomic changes, the Hydrophilus 

 and Hydrochara of the following key ure equivalent 

 to the Hydrous and Hydrophilus, respectively, of the 

 original keys mentioned above. H.B.L. 



1. Only 2 styli present on anterior margin of pronotum, 

 1 on each side, and a small group of styli present 

 beneath each anterior angle of pronotum 



Helophorus Fabricius 1775 



— Anterior margin of pronotum differently outfitted, 

 generally with a transverse row of more than 2 styli 

 {Hydrophilus, however, with only a small group of 

 styli at each anterior angle) 2 



2. Hind wings not visible dorsally; 2nd to 7th abdominal 

 segments each with a transverse row of 4 or 6 styli 

 on the tergite and 1 stylus on each pleurite (fig. 13:30rf) 

 3 



— Hind wings partly visible dorsally, not entirely covered 

 by posterior edges of fore wings; 2nd to 7th abdominal 

 segments each with a transverse row of 4 or 6 styli 

 on the tergite and 1 stylus on each pleurite 4 



3. Cerci of about same length as 9th abdominal segment, 

 placed closely together, slender, with a little dark, 

 hard tip bearing a seta; cerci indistinctly multiarticu- 

 late Cercyon Leach 18 17 



— Cerci much shorter than 9th abdominal segment, 

 conical and 2-segmented . . Sphaeridium Fabricius 1775 



4. Cerci long and distally provided with some minute 

 chitinous scales, or slightly bifid (fig. 13:396); either 



1 pair of supraorbital and 16 pronotal styli, or with 



2 pairs of supraorbital and 32 pronotal styli 5 



— Cerci not bifid, nor with scales distally; 2 pairs of 

 supraorbital styli (except in Hydrobius fuscipes which 

 has none), and 18-24 pronotal styli 7 



5. Styli on dorsal surface of abdomen in transverse rows 

 of 4 on each segment; spiracles partly concealed by 

 lateral tubercles 6 



— Styli on dorsal surface of abdomen in transverse rows 

 of 6 on each segment; spiracles not concealed, no 

 tubercles; 2 pairs of supraorbital styli, 32 pronotal 

 styli in all Hydrochara Berthold 1827 



6. Size large, length 25 to 30 mm.- 1 pair of supraorbital 

 styli (fig. 13:39a), and 16 pronotal styli in all 



Hydrophilus Geoffroy 1762 



— Size smaller, length 15 mm. or less; no supraorbital 

 styli (fig. 13:396), 26 pronotal styli in all 



Tropisternus Solier 1834 



7. Tergites of 2nd to 7th abdominal segments each with 

 a transverse row of 6 styli and 1 pleural stylus on 

 each side; 24 pronotal styli 8 



— Tergites of 2nd to 7th abdominal segments each with 

 a transverse row of 4 styli and 1 pleural stylus on 

 each side; pronotal styli frequently fewer than 24 . . . 9 



8. Styli short; terminal seta much longer than stylus 

 itself; anterior margin of pronotum with a row of 10 

 styli Paracymus Thomson 1867 



— Styli and terminal setae of nearly equal length, or 

 styli longer than terminal setae; anterior margin of 

 pronotum with a row of 6 or 8 styli, the external styli 

 of anterior row in a lateral position 



Cymbiodyta, Helochares, Enochrus 



9. Supraorbital styli only vestigial; 20 pronotal styli 

 in all; cerci long, finely articulated and tapering 

 (species fuscipes L. of genus) 



Hydrobius Leach 1815 



— With 2 pairs of well-developed supraorbital styli (fig. 

 13:39c) 10 



10. Eighth abdominal segment with 4 sharp, upcurved, 

 triangular processes posteriorly; cerci not articulated 

 Laccobius Erichson 1837 



— Eighth abdominal segment without triangular processes 

 posteriorly; cerci articulated distally (fig. 13:39c) 

 Berosus Leach 1817 



