1920] Richmond, Studies on the Biology of the Aquatic Hydrophilidoe 73 



the third segment is about as long as the first two together and nearly as wide; each 

 bears a few slender seta?, the terminal segment with a group of sense-cones at its 

 extremity. 



Labium slightly exceeding the inner distal tooth of the mandible; submentum 

 small; mentum and palpiger cylindrical and about the same size; mentum with short, 

 stout setae mounted on tubercles; palpiger with a longitudinal row of three distal seta? 

 on each side of the median line and an additional pair just inside the middle pair of 

 the latter row; palpus with first segment short, second segment about three times as 

 long and bearing sense-cones and seta? at its tip as well as at its base; ligula present 

 and nearly as long as the second segment of the palpus. 



Prothorax with sides slightly rounded, a little wider than the head; anterior 

 margin of pronotum fringed with a row of minute seta? set close together; epicranial 

 suture present; presternum with two fairly large sclerites in front of the coxa? touch- 

 ing along the median line but not highly chitinized; meso- and metathorax shorter 

 than the prothorax and about the same size as each other; the two sclerites of the 

 mesonotum large, with the anterior margin of the Avhole concave; two triangular 

 sclerites present in the pro-mesotergal suture; the spiracles on tubercles at the externo- 

 frontal angles of the mesothorax; metanotum with two pairs of elongate sclerites; 

 the caudal pair smaller and each with a prominent seta on its inner half. 



Legs short, a little longer than one-half the width of the thorax but with just the 

 distal end of the tibia? and tarsi showing from above; coxa? transverse; femora a 

 little longer than the tibia?; tarsi claw-like, shorter than the latter, bearing a promi- 

 nent inner seta, and another less prominent one towards the base; the two anterior 

 coxa? are closer together than the four posterior coxa?, which are about the same dis- 

 tance apart. 



Abdomen with eight distinct segments only slightly narrowed caudally, ninth 

 and tenth segments forming the atrium. The first seven tergites similar and each 

 with two transverse folds while the intersegmental membrane has only one. The 

 pra?scutum of each of the first seven tergites bears a pair of small, oval, chitinized 

 patches, the first pair being more prominent and elongate than the other six. A 

 prominent lateral tubercle present on both the segment and the membrane, the 

 one on the former being larger and more rounded than that on the latter. Below the 

 lateral tubercle of the segment there are two others. The tubercles on the folds are 

 hard to make out but are arranged in transverse rows as follows : six on the first fold 

 of the segment, the middle pair united by a small narrow fold; eight on the second 

 fold; and six on the intersegmental .membrane, the middle pair united by a small 

 narrow fold. The pair of tubercles on each side of the middle pair of tubercles of the 

 second fold bear a seta. Each spiracle situated between the outer pair of tubercles 

 of these first two folds. The eighth tergite represents the superior valve of the 

 stigmatic atrium. The structure of the atrium is similar to that of Laccobius. The 

 caudal border of the superior valve is nearly straight, slightly rounded in the middle. 

 The procerci and especially the mesocerci are quite prominent; the lateral seta of 

 each is slender but strong and slightly wavy. 



Full-growx Larva. — Length, 3.76 mm. (5.11 mm. extended); width at the 

 fourth abdominal segment, 1.21 mm.; depressed. Light yellowish; head and thorax 

 darker than the abdomen with the exception of the abdominal tubercles, which are 

 brownish and more pronounced than in the first instar. The tubercle on each side of 

 the middle pair of tubercles on the second fold of each segment is the most prominent 



