1920] Richmond. Studies on the Biology of the Aquatic Hydrophilidce 27 



Anal segment cylindrical, longer than wide, and banded with chitin, the tip 

 membranous, a transverse row of setae anterior of the caudal border of the band and 

 a terminal pair of stout, recurved hooks directed downward. 



4. Hydroscaphinae 



Eggs laid singly without a covering of silk. 



Larva with inclined head; antennae with points of insertion situated nearer the 

 externo-frontal angles than those of the mandibles; epicranial sutures present; 

 ocular areas round, convex and in groups of five more closely aggregated than with 

 the other primitive larva?; labrum well developed but clypeus 1 not present; mandibles 

 small each with a lacinia mobilis and concealed from above by the labrum; maxilla 

 primitive with an inner lobe; labium with short palpi; labium and maxillae inserted 

 in a furrow on the under side of the head; gula well developed and attaining the 

 occipital opening. Xine complete abdominal segments, and a distinct but reduced 

 tenth segment, the chitinized portion of all ten forming a continuous ring. Tracheal 

 gills present on several segments. Spiracles reduced so that the openings cannot be 

 seen. Cerci absent. 



5. Hydrochoinae 



Egg-case flat with a single egg enclosed. Larva with head inclined, antennae 

 with then points of insertion situated nearer the externo-frontal angles than those 

 of the mandibles are; epicranial suture absent; ocular areas oval and in groups of 

 six, closely aggregated; labro-clypeus very much reduced, the epistoma apparently 

 at the anterior margin of the head; mandibles prominent, each with a slender distal 

 piece terminating in a stout seta; and with a lacinia mobilis; maxilla palpiform, the 

 inner side of the stipes with a small swelling; palpifer without a rudimentary lobe; 

 labium with short palpi and ligula absent ; labium and maxillae inserted in a furrow 

 on the under side of the head; gula small but attains the occipital opening; eight 

 complete abdominal segments, and each with a dorsal and ventral plate. Ninth and 

 tenth segments reduced. Type of breathing pseudo-metapneustic and the bifore 

 spiracles are poorly developed. 



Hydrochous Leach 

 As with the genus Helophorus, we find most of the species very 

 closely related. However, the rare Hydrochous scabratus, with its promi- 

 nently tubercled elytra, is a well-marked species. The most common 

 species is H. squamifer but two closely allied and undetermined species 

 (possibly undescribed) are almost as abundant. A few specimens of 

 H. excavatus '? have also been recorded. The only genus with which 

 the collector might confuse the adult is Helophorus but the former is 

 easily differentiated in the water by the angular form and blackish 

 color, which has a decided tendency to be iridescent. The seven- 

 segmented antennae and discal foveas of Hydrochous clearly separate it 

 from Helophorus with, its nine-segmented antennas and discal sulci. 



'The olypeus may have fused with the labrum. 



