TRICHOPTERA 



569 



the log-cabin type. Some individuals make a case composed of small 

 chunks of bark (Fig. 702, a); others make cases composed almost 

 entirely of shells of water snails (Fig. 702, 

 b) . Different combinations of these types 

 are frequently found. 



Some larv^ of this family make cases 

 of leaves; these are either fastened so 

 as to form a flat case, or arranged in 

 three planes so as to form a tube, a cross- 

 section of which is a triangle. 



Larvs of the genus Neophylax make 

 cases of sand with large ballast stones at 

 the sides; these are similar in form to 

 those made by Goera calcarata of the next 

 family, but are more slender, smaller, and 

 made of lighter material. 



Family SERICOSTOMATID^ 



Fig. 702. — Case ot Limnophilus 

 combinatus. (After Lloyd.) 



Fig. 703. — Case of 

 Helicopsyche. 

 (From Lloyd.) 



The larv« are caterpillar-like, and are found in streams and lakes. 

 The cases made by members of the different genera 

 differ greatly in form; the three following are our 

 best-known examples. 



Helicopsyche bor edits. — The larvae of this species 

 are found in stony streams and along the rocky shores 

 of lakes. They make a spiral case of grains of sand 

 (Fig. 703). This case so closely resembles that of a 

 snail in form that it has been described as the shell 

 of a mollusk. When about to pupate, the larvse fasten 

 their cases to a submerged rock; at this time they 

 display a gregarious instinct, large numbers of them congregating 



within a very small area. 



They are more easily found 



at this time than in their 



earlier stages when they 



are living free among the 



sand and gravel of the bot- 

 tom of the stream. 



1 Goera calcarata. — ^The 



Bxvse. of this species are 



found in the riffles of 



streams and on stones in 



wave-beaten areas of lake 



shores, where they crawl 



over the surface of bare, 



current-swept rocks. The 



Fig. 704.— Case of Goera larval case (Fig. 704) is a 



(After ^ubg made of fine grains of 



sand on each side of which 



calcarata. 

 Lloyd.) 



Fig. 705. — Case of 

 Brachycentrus 

 nigrisoma. 

 (From Lloyd.) 



