WATER BEETLES IN RELATION TO PONDFISH CULTURE. 



319 



The mandibles are asymmetrical, the left one with a single large tooth on the inner margin, the right 

 one with two. The distal portions of the two mandibles are about the same size and curvature, and 

 each has a row of well-defined teeth extending from its base nearly to the tip. The large tooth on the 

 left mandible has two minute spines on its proximal margin, while the same margin of the distal tooth 

 on the right mandible has a row of four saw teeth. The proximal tooth on the right mandible is much 

 smaller than the distal one and is unarmed. By comparing the figures here given of the mandibles with 

 those published by Richmond (1920) of the mandibles of perplexus it will be seen that the former are 

 much more prominently toothed and that the proximal tooth on the right mandible is much nearer to 

 the distal one, as Richmond (1920) himself stated. 



The maxillse are long and stout. When the tips of the mandibles just touch each other in front of 

 the head, the antennae, the mandibles, and the labial palps all reach the same level, which is about 

 the center of the palpiger of the maxillse. Thus, the distal half of the palpiger and the whole of the 

 palps project beyond the other appendages. The cardo is fused with the stipes, and the junction of 

 the two is indicated by constrictions on the lateral margins. The stipes is large and stout and not much 

 narrowed distally; it is one-half longer than the palpiger and palpus together, with two large setse on 

 the outer margin just beyond the center. The palpiger is about half the diameter of the stipes, its 

 length to its width as 9 to 14. At its inner distal corner is a club-shaped process as long as the first joint 

 of the palpus and tipped with two setae. The palpus is three-jointed, the joints increasing in length 

 distally in the proportion of 5, 7, and 9. The basal joint has a single seta on its dorsal surface near the 

 outer margin, the second joint has one on the inner margin, and the terminal joint is tipped with two 

 setae and three sense cones. 



The labium is proportionally large, with a pentagonal gula one-half wider than long; its postero- 

 lateral margins are four times the length of the antero-lateral ones. The submentum is small; the 

 mentum is barrel-shaped, about as long as wide. The palpiger is dome-shaped and three-fifths as long 

 as the mentum; the ligula is a little longer than the basal joint of the palps and slightly enlarged at its 

 tip. The labial palps are two-jointed, the terminal joint three times as long as the basal and tipped 

 with setae and sense cones, but without any setae at its base. 



The prothorax is as long as the head and one-fourth wider, with strongly convex sides; the mesothorax 

 and metathorax diminish in length, but are as wide as the prothorax. The abdomen is slightly narrower 

 than the thorax, the first seven segments distinct and similar, slightly narrowing posteriorly, the eighth 

 and ninth segments rudimentary, representing, respectively, the superior and inferior valves of the 

 stigmatic atrium. Spiracles present on the mesothorax, metathorax and the first seven segments of the 

 abdomen. These abdominal segments also bear laterally one large and two small tubercles on either 

 side and a row of four across the dorsal surface, all armed with long setae. On the ventral surface each 

 segment from the third to the seventh inclusive carries near each lateral margin a prominent tubercle, 

 which is armed with recurved spines instead of setae and serves as a proleg. 



The mature larva. — When mature, the larva is 6.40 mm. long and 1.35 mm. wide at the first three 

 abdominal segments. The head, the thorax, and the anterior abdomen are light brown, the posterior 

 abdomen is gray. The head is 0.45 mm. long and 0.55 mm. wide; the first joint of the antenna is nearly 

 as long as the second; the serrate flap of the labrum is retained and becomes a little more prominent on 

 the right side, and thereby asymmetrical. The serrations on the terminal blades of the mandibles are 

 completely retained, but those on the proximal margin of the median teeth have entirely disappeared. 

 Neither the maxillae nor the labium have changed. 



This larva crawls fully as far from the water's edge as the much larger Tropisternus larva and locates 

 its pupal chamber in rather dry mud, pupation taking place almost as soon as the pupal chamber is 

 completed. 



Description of the pupa. — -General form elongate-ovate, 4.50 mm. long, exclusive of the cerci, and 

 1.90 mm. wide through the prothorax, the abdomen much narrowed posteriorly. Entirely white except 

 the eyes, which are dark brown, almost black, and the cerci and styli, which are light brown. 



Head smooth with two supraorbital styli on either side, but no tubercles near the vertical margin. 

 Pronotimi somewhat three-lobed anteriorly, its posterior margin straight but not indented in front of 

 the elytra. Twenty-four styli, 10 on the lateral and anterior margins, the 2 on the median lobe 

 much longer than any of the others, 8 on the posterior margin, 2 on the median lobe posterior 

 and outside of the long anterior ones, and 4 in a curved transverse row behind them. Mesonotum and 



