1920] Richmond, Studies on the Biology of the Aquatic Hydrophilidce 31 



7. Hydrophilinse 



Egg-cases characterized by their horny mast and comparatively larger size. Larva 

 with elevated head; antenna? with points of insertion farther from the externo-frontal 

 angles than those of the mandibles; second segment without an antennal appendage; 

 epicranial suture absent or very short ; ocular area flat, elongate and closely aggre- 

 gated although distinctly separated; both labrum and clypeus almost entirely 

 reduced, the front margin nearly straight and with only a few small teeth. Mandibles 

 prominent, sharply pointed, furrowed internally and with inner teeth; maxilla 

 palpiform, slender, the stipes longer than the palpifer and palpus together, palpiger 

 with an inner rudimentary lobe; labium with palpus longer than in the primitive 

 genera, the second segment distinctly longer than the first; ligula present, labium and 

 maxilla? inserted at the anterior margin of the under side of the head; gula reduced 

 and not attaining the occipital opening. Legs provided with fringe of seta?. Eight 

 complete, non-chitinized abdominal segments; ninth and tenth reduced. Type of 

 breathing pseudo-metapneustic and with poorly developed bifore spiracles. Tracheal 

 gills, if present, not well developed. Cerci reduced but two-segmented. Prostyles 

 present or absent. 



Hydrophilus Leach 



There are fewer species in this genus than there are in Hydrous, but 

 the members of Hydrophilus are more equally distributed over the world. 

 One of the four American representatives, H. obtusatus, occurs at Ithaca. 



The well-known European species, H. caraboides, was one of Lin- 

 naeus' species and Roesel in 1749 knew some of its larval instars besides 

 the pupa. Lyonet was the first to describe the egg-case and Schiodte 

 later gave the entire life history. The egg-case and young larva of H. 

 obtusatus were figured by Bowditch in 1884. He gave a very interesting 

 account of its biology but did not observe the pupa. The full-grown larva 

 and pupa were later described by Wickham but the figures are of little 

 value and the descriptions meagre. Although it varies in size, it is our 

 second largest hydrophilid and is intermediate, in this respect, between 

 Tropisternus and Hydrous. The beetle is very clumsy and in no way 

 approaches the two other genera of this subfamily in aquatic adaptation. 

 It is most frequently found in leaf-filled pools, mud holes, at the water's 

 edge under debris or clumps of grass, or in pools overgrown with vegeta- 

 tion. Several adults are often taken together in such situations, but 

 only isolated specimens are usually recorded. 



Hydrophilus obtusatus Say 



Plate I, Figures 1, 2, and 6; Plate VI 



The egg-cases of H. obtusatus appear in late May and early June but 

 are not often reported. The fact that they are usually covered with a 



