294 



BUULETIN OF THE BUREAU OF FISHERIES. 



lateral fringes of the last two segments. There is a pair of oblong chitin plates on the mid line of the pro- 

 thoracic sternum, which together are about half the length and width of the segment. The tracheae 

 show through in the last two segments as longitudinal dark brown lines. 



Head obovate, widest through the eyes, its length to its width as 11 to 8, narrowed into a short neck 

 posteriorly. Epicranial suture more than half the entire length; frons triangular with convex sides and 

 prominent knobs at the anterior angles. The fringe along the frontal margin is made up of four rows of 

 club-shaped processes diminishing in size from in front backward . There are no laciniate laminae as in the 

 omaticollis larva, nor any sharp spines as in the Acilius larva. The two large eyes protrude as black hemi- 

 spheres from the dorsal surface ; only two of the other four are visible in dorsal view, and they are minute. 



The prothorax is twice as long as wide, the posterior margin a little more than half as wide again as 

 the anterior, the sides nearly straight. The mesothorax and metathorax increase in width, the latter 

 being twice as wide as long. The abdominal segments increase regularly in length ; the first two increase 

 slightly in width, the third is the same width as the second, and the remaining segments diminish regu- 

 larly in width. The last segment is broadly rounded at the tip and carries two slender cerci on its ventral 

 surface a short distance in front of the end. 



The antennae are six-jointed, the second and fourth joints short and subspherical, the sixth joint 

 also short but finger-like. The mandibles have a fringe of long hairs on the outer margin near the base.^ 

 The maxillae are curved considerably and have a decided hunchbacked appearance; the spinous process 

 is acuminate and has a row of minute hairs along its inner margin; the inner distal comer is sharply 

 rounded and bears a tuft of small spines, which are continued down the inner margin. There are two 

 longitudinal rows of stiff spines on the dorsal surface, the outer one strongly curved to follow the con- 

 tour of the outer margin, the inner one much less curved. The palps are four-jointed, the third 

 joint spherical, the basal joint shorter than the second and fourth, which are about equal (fig. 62, p. 292). 



The labium is narrow and elongate; on the dorsal surface the palpiger has a raised and papillated 

 margin on all four sides, covered with minute hairs and with a row of short spines across the distal margin. 

 The ventral surface is smooth and bare, except for two long setae near the base of the ligula. The palps 

 are two-jointed, the joints about the same length, the basal joints with a row of spines along their outer 

 margins, the terminal joints with a few spines on the outer margins at the base and on the inner margins 

 at the tip. The ligula is long, narrow, and tapering, and carries at its tip two short, divergent, two- 

 jointed spines. The legs are long and slender and well supplied with swimming setae. 



When taken from the pupal chamber just before pupation, the larva has diminished to 15 mm. in 

 length, the width has increased to 2.9 mm. The color is now a uniform brown on the dorsal surface 

 and light yellowish-white on the ventral surface, except the last two segments, which are brown. The 

 head also is brown on both surfaces, the sclerites have lost their lateral dark lines, and the spiracles 

 show through them as black dots. The four small eyes are black, the two larger ones have a decided 

 reddish tinge. 



Pupation — When the larva is fully grown, it selects a spot on the land that is well shaded and where 

 the mud is rather soft. Here a foot or more from the water's edge it constructs its pupal chamber, which 

 is subspherical in shape and 12 to 14 mm, in diameter. It is made of little pellets of mud stuck together 

 rather loosely and rests upon the surface of the ground Its walls are so thin and friable that it is prac- 

 tically impossible to pick it up intact, except by cutting out a section of the mud beneath it. The 

 building of the chamber occupies one to one and a half hours, and when it is completed the inside is 

 smoothed by the larva rubbing it with its body The larva then folds the last two segments of the body 

 forward and the head and thorax backward above them, like the Dineutes larva, and rests upon its back 

 on the bottom of the chamber. The prepupal period lasts one and a half to two days. At the end of 

 that time the skin splits along the dorsal mid line from the base of the head to the penultimate abdominal 

 segment and is flattened out against the inner wall of the chamber, to which it adheres firmly. The pupa 

 emerges upon its back on the bottom of the chamber and rests there for 24 hours, then it reverses its 

 position and rests upon the long styli on the pronotum and the cerci at the posterior end of the abdomen, 

 the dorsal surface uppermost and the body strongly arched. 



1 This fringe was accidentally omitted from Fig. 60; it should be the same as in Fig. 61. 



