June, 1914-] Lloyd: Lepidopterous Larv^ in Rapid Streams. 147 



times on the edge, the pupal cases are located. The cases, pi. 2, figs. 

 5, 6, are oval in shape, about three quarters of an inch long and half 

 an inch wide and are elevated about one tenth of an inch above their 

 support. Their roofs are flat and are supported by perpendicular side 

 walls which are perforated at each end by six or more clean-cut holes 

 to permit free circulation of water. The inner pupal case consists of 

 a sheet -of loose-spun silk. Radiating threads attach the cocoon to 

 the roof but, as in the case of the larval sheets, there is no silk floor 

 over the surface of the rocks. The pupal cases, unlike the larval 

 sheets, are spun of thick inflexible layers of silk and, also unlike the 

 larval sheets, become thickly coated with diatomaceous ooze. 



Period of Emergence. — The first adults were seen August tenth. 

 By August seventeenth they had reached their maximum numbers, 

 fairly swarming as one walked through the vegetation along the 

 water edge, but seldom occurring more than a few yards from the 

 stream. By August twenty-eighth no adults could be found. 



Description of Larva and Pupa. 



Larva.- — The length of mature larva, PI. Ill, fig. i, is ten to eleven 

 mm., its form is depressed tapering gradually from its head to the 

 end of its tenth abdominal segment. Its color is dark straw-brown. 

 The unbranched, hairlike tracheal gills form a double row along each 

 side of the thorax and abdomen. The upper line of gills is plainly 

 suprastigmatal in position and the lower line is infrastigmatal. The 

 arrangement and distribution of the gills makes it impractable to 

 apply the other terms, anterior- and posterior-stigmatal, used by 

 Forbes in " The Aquatic Caterpillars of Lake Quinsigamond," Psyche, 

 December, 1910. 



Head. — Almost circular in outline, heavily chitinized, its diameter 

 at least as great as any segment of the body. A narrow, heavily 

 chitinized band, PL III, fig. 4, along the posterior side of the frons 

 forming a conspicuous dark brown V shaped mark. A similar band 

 borders the hind margin of each epicraniuni. The middle pair of 

 setse on each lobe of the labrum, PI. Ill, Fig. 2, are modified into thin, 

 transparent, fan-like plates with irregular margins at the distal, or 

 broad, end of the fans. Their bases are heavily chitinized, circular 

 in outline and resembling the bases of ordinary setje. They arise 



