1920] Richmond, Studies on the Biology of the Aquatic Hydrophilidoe 33 



Antennae slender, extending forward about as far as the tips of the mandibles; 

 first segment much longer than the second and third together, slightly constricted 

 near the base, a little crooked and with a few short conical spines on its inner surface; 

 second segment bent inwardly a little, slightly longer than the terminal segment and 

 with a disto-medial seta; latter segment more slender and possessing a few distal 

 set re. 



Mandibles symmetrical, 1 prominent, elongate, sharply pointed at their tips and 

 with their inner surfaces grooved; each mandible with two inner teeth, the proximal 

 tooth smaller than the distal and slightly bifid; distal tooth furrowed on its inner 

 surface, and the furrow is continuous with a furrow surrounding the proximal tooth. 



Maxillae slender and with joint-like palpifer; stipes swollen near its base, slightly 

 bowed, longer than the palpifer and palpus together and its inner surface with a row 

 01 five setae, the basal four fairly stout; palpifer with a small chitinous appendage 

 bearing a terminal seta at its disto-medial angle; about twice the length of the 1st 

 palpal segment but only very slightly wider; palpal segments all about the same 

 width and bearing the relation of 7, 13, and 20; terminal segment with a single distal 

 sense-cone. 



Labium prominent, palpus nearly attaining the distal end of the stipes, its first 

 segment short, the second the same width but about five times as long and with 

 terminal sense-cones ; ligula well developed, more than twice as long as the first palpal 

 segment, cylindrical, only slightly tapering, chitinized except tip; palpiger four- 

 elevenths longer than wide, sides parallel; mentum cordiform, anterior angles pro- 

 nounced and acute; submentum extremely transverse, small and joint-like. 



Prothorax narrower than the head, sides parallel; pronotum bearing a few 

 scattered setae; entirely chitinized except at the anterior margin and the sagittal line, 

 which continues through the thorax; ' a large ventral sclerite present in front of the 

 prothoracic coxae. 



Meso- and metathorax similar to each other, a little wider than but less than 

 one-half as long as the prothorax, each Avith a pair of fairly large, irregular subtri- 

 angular sclerites and a lateral tubercle. A bifore spiracle present in each antero- 

 lateral angle of the mesothorax while, corresponding in position to it, there is a 

 small tubercle on the metathorax. Pro-mesothoracic and meso-metathoracic sclerites 

 are present and are small, elongate, horizontal plates. 



Legs about twice as long as the width of the thorax; segments beginning with 

 coxae bear the relation of 35, 12, 35, 25 and 15; tarsi well developed, claw-like, and 

 each with two inner setae, one dorsal to the other. 



Abdomen with eight distinct segments, narrowed posteriorly, ninth and tenth 

 rudimentary. The first seven tergites similar, each with two very much reduced, 

 oval, chitinized patches on the proscutum, the first pair larger than the others, and 

 four small but conspicuous tubercles in a transverse row across the posterior or second 

 fold of the scutum, each bearing a seta. Each tergite consists of three transverse 

 folds while the intersegmental membrane has only one; sternites with similar arrange- 

 ment except that there is a longitudinal fold on each side of the three transverse folds. 

 Seven pairs of rudimentary bifore spiracles and seven pairs of pleural appendages, 

 equally long (0.48 mm-.), on the first seven segments. A small dorsal tubercle at the 

 base of the appendage. The eighth tergite represents the superior valve of the stig- 



'In //. glacus the mandibles are asymmetrical. The left mandible possesses only a single inner 

 tooth. 



