280 



BULLETIN OF THE BUREAU OF FISHERIES. 



in the center a short and narrow ligula, with a tuft of setae on either side (fig. 27). Each palp is four- 

 jointed, the second joint with a tuft of setse on the inner margin at the distal end, the terminal joint tipped 

 with two tiny sensory processes. 



The sclerite of the prothorax extends around the lateral margins and onto the ventral surface as far 

 as the base of the legs ; the sclerite of the mesothorax stops at the lateral margins ; and the sclerite of the 

 metathorax stops at the base of the lateral ridge. These three sclerites do not quite reach the posterior 

 margins of their respective segments. The sclerites of the first six abdominal segments are very short 

 and narrow, covering less than a fifth of the length and about half the width of each segment. The scle- 

 rites of the last two segments are entire, covering the lateral and ventral as well as the dorsal surfaces. 

 Each sclerite of the first six abdominal pairs has two longitudinal dark stripes, and the brown of the dorsal 

 surface of each segment is deepest along the lateral margins. The last segment ends in two tracheal 

 tubes which project slightly. Just in front of the tip on the ventral surface is a pair of tiny triangular 

 processes, each bearing two long setae (fig. 29). The anus opens on the ventral surface about a quarter 

 of the length of the segment in front of its tip. The sides of the thorax and the lateral ridges along the 

 first six abdominal segments are clothed with short, scattered hairs of unequal length. On the dorsal 

 surface of the lateral ridges near the anterior margin of each of the first six abdominal segments and on 

 the sides of the meso and meta thorax are the spiracles. Behind the spiracles, near the longitudinal 

 center of each segment, is a brown pigment spot. From the center of each of these spots, from a corre- 

 sponding position on the prothorax and from each of a row of tiny spots across the dorsal surface near the 

 anterior margin of the prothorax projects a plumose hair (fig. 28). The base of each of these hairs is a 

 single thick trunk, which is divided and subdivided dichotomously until there are from 12 to 20 resultant 

 branches. 



Pupation. — A larva was found on the bank of pond 5D July 24, about 2 feet from the water's edge. 

 It was hunting for a place to pupate and so was brought into the laboratory and placed in an artificial 

 pupal chamber, whose size was proportioned to that of the larva. At first it stretched itself at full length 

 upon the floor of this chamber, bending its head downward at right angles to the thorax and burying its 

 mandibles for their entire length in the mud. It remained in this position for a week, scarcely moving 

 at all, and then some water was put in the bottom of the jar and allowed to soak up through the floor of 

 the chamber. Apparently this was what it was waiting for, since just as soon as the mud became soft 

 enough it built a new pupal chamber inside of the artificial one. Although the larva was 75 mm, in 

 length this new chamber was only 35 mm. long, 30 mm. wide, and 25 mm, high, outside measure. It 

 was made of mud pellets half the size of a pea, which were cut out by the mandibles, rolled into form 

 between the mandibles and labium, and then pressed into place, one against another. 



Inside of this chamber the larva rested upon its back and folded its body in exactly the same man- 

 ner as the Thermonectes larva, the posterior portion of the abdomen being turned forward above the an- 

 terior portion, and the head and thorax turned backward above the two. It remained in this position 

 until August 8 before pupating, when the skin split along the dorsal mid line from the base of the head 

 to the posterior margin of the sixth abdominal segment. The contents of the larval head and of the 

 last two abdominal segments were withdrawn in toto, and the skin was then flattened back against the 

 inside of the wall of the chamber. The adult beetle emerged August 22. 



Another larva was obtained from a loosely constructed chamber close to the water's edge . This cham- 

 ber also was made of mud pellets, but fragments of leaves and small sticks were mixed with them and the 

 walls were so fragile that they could not be removed to the laboratory. Accordingly the larva was placed 

 in an artificial chamber, which was made much smaller, profiting by previous experience. It was evi- 

 dently still too large, however, for the larva constructed a new and smaller one inside of it, in which it 

 pupated August 6, and the adult beetle emerged August 19. 



Description of the pupa. — On fijst emerging from the split larval skin the pupa is creamy white in 

 color, and its skin is shiny like the wings of a teneral dragonfly. Its total length is 35 mm. and the 

 greatest width 13 mm. The only pigment visible is a lavender band around the anterior margin of each 

 compound eye, and just behind this the six larval eye spots, which are black. Five of these spots are 

 arranged in a row close to the posterior* margin of the lavender band; the sixth one is a little farther 

 back, between the second and third spots of the row. The first (dorsal) spot in the row and the sixth 

 one are elongated at right angles to the longitudinal axis of the head, the others are circular. 



