1920] Bichmond, Studies on the Biology of the Aquatic Hydrophilidce 83 



10. Projection distinctly tubular proximally. Case proper nearly spherical. 



Laccobius; Anccena. 



Projection not distinctly tubular proximally. Case somewhat chestnut-shaped. 



Contour of eggs visible at the cap end Berosus. 



11. Filament broader and often surrounding the cap end. Case nearly spherical. 



Hydrobius. 

 Filament narrower. Case proper more elongate and smaller Philydrus. 



12. Cases (free floating) noticeably larger. Cap hatchet-shaped and not covering 



entire end 13. 



Cases (attached to aquatic vegetation) smaller. Cap round and covering entire 

 end Tropisternus. 



13. Case naked, spine-like projection stout Hydrous. 



Case enwrapped in a leaf, spine-like projection slender and tip often bent over. 



Hydrophilus. 



14. Eggs laid on damp leaves (blanket-like covering of silk) Phcenonotum. 



Case carried on the under side of the body by the female 15. 



15. Case attached to the hind legs 16. 



Case held in place by the elytra and modified abdominal segments. 



Epimetopus; Choetarthria? 



16. To the femora only Helochares. 



Tc the femora and tibiae Spercheus. 



17. Egg-mass deposited near the water, usually under fallen leaves 18. 



Egg-mass deposited in dung or damp earth 19. 



18. Egg-mass usually larger. Number of eggs varies from 15-43 Cymbiodyta. 



Egg-mass usually smaller. Number of eggs varies from 10-15 Paracymus. 



19. Egg-mass larger .' Sphceridium. 1 



Egg-mass smaller Cercyon (?) . 



Key for the Identification of the Larvae 



1 . Nine complete abdominal segments, the tenth reduced but distinct. Integument 



noticeably chitinized 2. 



Eight complete abdominal segments, the ninth and tenth reduced and forming 

 a stigmatic atrium (except in Berosus in which the atrium has not developed). 

 Integument not noticeably chitinized (except in Hydrochous) 6. 



2. Head inclined ; epicranial suture present ; ocular areas in groups of five ; mandible 



with lacinia mobilis: maxilla primitive with prominent inner lobe; labium 

 and maxillae inserted in a furrow on the under side of the head; gula well 

 developed and attaining the occipital opening. Cerci absent or well developed 

 and two-segmented 3. 



l No account is given of the eggs of Sphceridium or Cercyon except the situation in which they are 

 laid. I have observed only a single mass of Sphceridium eggs. 



