218 THE CANADIAN ENTOMOLOGIST. 



la. Larvae thysanuriform. (F"ig. 1.) Abdomen of nine segments; 

 prolegs not fused in median line to form an apparent tenth 

 segment.* (Fig. 3.) No tubercles on first abdominal 

 segment. No prosternal horn. No lateral line. Tracheal 

 gills generally absent; rectal gills generally present, but not 

 always everted 2 



lb. Larvae cruciform or sub-eruciform. (Fig. 2.) Basal segments 

 of prolegs fused in median line to form an apparent tenth 

 abdominal segment. (Fig. 4.) Tubercles present on first 

 abdominal segment. Prosternal horn often present. (Fig. 

 35.) Lateral line present, but sometimes very light. No 

 rectal gills; tracheal gills generally present 10 



2a. Abdomen very much wider than the thorax. Small larvae 

 with portable cases of silk Hydro ptilidcB. 



2b. Abdomen not very much wider than thorax. Cases when 

 present not of silk only 3. 



3a. Chitinous shield present on the dorsal surface of the ninth 

 abdominal segment. (Fig. 7 and 8) 4. 



3b. No chitinous shield, on the dorsal surface of the ninth ab- 

 dominal segment. (Fig. 3) 5. 



4a. Prolegs well developed, free; claws of the prolegs long and 

 slender, without teeth on convex surface, but sometimes 

 with teeth on concave surface. Sometimes accessory claws 

 present at side of main ones. (Fig. 7) . Maxillary lobe long 

 and slender. (Fig. b.)...RhyacophilincB (Fam. RhyacophUidce). 



4b. Prolegs short; basal segments wholly chitinized and fused to 



the ninth abdominal segment in a nearly vertical position. 



Claw very long with small teeth on convex side. (Fig. 8.) 



Maxillary lobes short, broad, with many sense rods. (Fig. 6) 



GlossosomatuicE (Fam. RhyacophUidce) . 



5a. Branched tracheal gills present. (Fig. 12.) All three thor- 

 acic segments chitinized dorsally. Numerous bristles on 

 convex side of mandibles. (Fig. 13) 6. 



5b. No tracheal gills. Only prothorax chitinized dorsally (except 

 in EconomincB, where all three segments are chitinized). 

 Only two bristles on convex side of mandibles 7. 



In the Hydroptilidte there is an indefinite suture crossing the ninth segment 

 dorsally, giving somewhat the appearance of a tenth, but this family can easily 

 be set off by the general shape of the body (see 2a). 



