1882.] 69 [Clarke. 



water, the larvae nearly all die in the course of a few hours. 

 Occasionally however, one, more hardy than the others, will live 

 for several clays, or even two or three weeks. 



I have not looked for this species except in the neighborhood 

 of Boston, but I have received a net and larva from Mt. Desert, 

 Me. 



A very peculiar case is also made by another larva belonging to 

 the same family, Hydropsychidae, and the genus Plectrocnemia. 

 Cases of this kind are quite abundant in Stony Brook, near Bos- 

 ton, close to the Forest Hills station. Looking down into the 

 clear water, we see on the muddy bottom, dead leaves, sticks 

 twi^s, etc., covered with a thin film of mud. Among these are 

 some objects which appear like nearly erect twigs or leaf petioles, 

 but with a small hole in their apex. These are in reality tubes of 

 mud constructed by the Plectrocnemia larvae, and by working 

 the fingers about in the mud at the base of the tube, it can be 

 taken out, together with the part that lies concealed beneath. 



The typical form (fig. 3) is a tall, nearly cylindrical chimney, 

 from one to two inches long and one eighth of an inch in diameter, 

 about three-quarters of an inch pro. 

 jecting above the surface of the mud. 

 At the base of this chimney are one 

 or more lateral tubes, which for a 

 quarter of an inch are of the same 

 diameter as the vertical tube, but 

 then swell out into an oblong chamber ^ — ^ 



about half an inch long and a quarter 1 ^ ^ 



of an inch or more in the greatest / S ■ S 



diameter. Usually there is a small \/ 



hole at the end of this chamber, but x °' ' 



sometimes the chamber extends into another short piece of cylin- 

 drical tube which contracts to a small aperture at its termina- 

 tion. Whether these holes serve merely as an exit for the respi- 

 ratory current, or whether the larva uses them as doors I can- 

 not determine. Neither can I decide in which part of the case 

 the larva lives, whether in the vertical chimney or in the side 

 chamber ; but I have always found the pupa in a vertical position 

 in the upright shaft, its place being usually indicated by an 

 enlargement of the tube (fig. 4), These chambers have a smooth 



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