Nerve-winged Insects; Scorpion-flies; Caddis-flies 245 



Head elliptical, only pronotum (dorsal wall of prothorax) chitinized (horny and 

 dark), abdominal constrictions deep; cases of vegetable matter laid longitudi- 

 nally and forming a spiral, widening at front end PHRYGANEID^E. 



Head oval to circular, pronotum chitinized, mesonotum often, and metanotum some- 

 times chitinized, abdominal constrictions slight. 



Lateral fringe well developed; cases various LIMNOPHILID^E. 



Lateral fringe slightly developed; cylindrical case of sand or small stones. 



SERICOSTOMATID^E. 

 Larva with head projecting straight forward in line with the rest of body; tubercles 



and lateral fringe wanting; gill-filaments, when present, branched. 

 Abdomen much thicker than the thorax; case kidney-shaped, of small stones, or flat 



and parchment-like '. HYDROPTILID^E. 



Abdomen little if any thicker than the thorax. 



Third pair of legs a little longer than the first pair; no larval case. .RHYACOPHILID^E. 

 Third pair of legs about the same length as first pair; no portable larval case. 



HYDROPSYCHID^E. 



