1920] Richmond, Studies on the Biology of the Aquatic Hydrophilidce 41 



Labium prominent, almost attaining the tip of the left mandible; submentum 

 transverse and hinge-like; mentum longer than wide, arched below, its sides at basal 

 half slightly concave but at its distal half convex, the fronto-external angles produced 

 forward and prominent; palpiger much narrower than the mentum, its sides diverg- 

 ing anteriorly; hgula somewhat thimble-shaped, about the same size as the first pal- 

 pal segment ; the second segment of the palpus more than twice as long as the first 

 and slightly convex on the outer side. 



Prothorax narrower than the head; anterior margin nearly straight; proscutum 

 represented by two, fairly large, somewhat triangular sclerites. Sagittal line present 

 throughout thorax. Mesothorax slightly shorter than prothorax but just as wide; 

 the mesoscutal sclerites more triangular and smaller. A small bifore spiracle 1 present 

 in each spiracular area. Metathorax similar to latter but not quite as long. 



Legs very long, about two-fifths longer than the thorax is wide; coxae nearly as 

 long as the femora, the latter with swimming fringes; tibiae shorter than femora and 

 three-sevenths longer than tarsi. The tarsi bear two inner setae, one distal to the 

 other; tarsi claw-like and well developed. 



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

 rudiment ary. The first seven tergites similar and each divided into three transverse 

 folds, while the intersegmental membrane has only one. The second scutal fold 

 bears a transverse row of four small tubercles. Epipleurite and hypopleurite each 

 surmounted by a small tubercle, not distinctly separated but together forming an 

 elongate lateral lobe. First five sternites with three transverse folds and a longitudinal 

 fold on each side of them. Eighth tergite about as long and wide as the interseg- 

 mental membrane preceding. The dorsal region represents the superior valve of the 

 stigmatie atrium and bears a reduced plate, the slender anterior arms of which enclose 

 a median, elongate, non-chitinized area. The caudal margin of the eighth tergite 

 is minutely crenate towards the sides and is rounded in the middle. The rudiments of 

 the four lobes found in other Hydrophilinae are weakly indicated. There are two 

 small tubercles, one below and on each side of the middle lobe of this hind margin. 

 Procerci fleshy and quite prominent. The mesocerci are fairly prominent, as well as 

 the acrocerci. The median lobe of the ninth tergite is slightly bilobed. Lateral lobes 

 not prominent. The prostyles, belonging to the tenth segment, are nearly as long as 

 the seventh and eighth segments together (1.44 mm.) and are superficially annulate. 



Full-grown Larva. — Length, 40-54 mm.; width at the first abdominal seg- 

 ment, 9-12.5 mm. General color grayish or dirty whitish except reddish brown head, 

 sclerites, and legs. Head 6.5 mm. wide; 5 mm. long below; 3.1 mm. long above. 

 Antennae four-segmented, 2 a small segment about one-third the length of the third 

 segment having appeared between the first and second segments of the first-stage 

 antenna. Lateral expansions of the epistoma not prominent. Mandibles with tips 

 and inner teeth blunt. Terminal segment of maxilla only about half the penultimate 

 in length. Ligula dome-shaped, much shorter than the first palpal segment, which 

 is a little more than one-half the second segment of the maxillary palpus. Dorsal 

 surfaces of the mentum and palpiger with a few scattered setae. 



1 Matheson described a pair as present on the metathorax also but none were seen in the specimens 

 which I examined. 



s D'Orchymont considers that Sehiodte was mistaken when he called the antenna of Hydrous 

 four-segmented. There are Burely four in //. triangularis. 



