222 THE CANADIAN ENTOMOLOGIST. 



15a. Postsegmental gills on lateral line always covered with black 

 hairs. (Fig. 33). Prothorax only chitinized. One pair of 

 small bristle-bearing plates on mesothorax and on meta- 

 thorax Phrymneidcs. 



15b. Ciills never with black hairs. Thoracic armature not as in 

 15a 16. 



16a. Prothorax and mesothorax chitinized dorsally. Metathorax 

 membranous, bearing three pairs of small shields; median 

 anterior pair very small; second pair small, slightly laterad 

 and posterior to first; third pair largest, generally crescent- 

 shaped, lying laterad to second; all well supplied with 

 bristles. (Fig. 34) LimnophilidcE. 



16b. Thoracic armature not as in 16a 17. 



17a. Pronotum chitinized. Mesothorax bearing two or three pairs 

 of heavily chitinized plates, metathorax with two or four 

 pairs of smaller plates 18. 



17b. Pronotum chitinized. Mesonotum and metanotum mem- 

 branous, or at most only weakly chitinized 19. 



18a. Anterior angles of pronotum produced into pointed processes. 

 Head retractile. Two or three pairs of plates on mesothorax; 

 four pairs on metathorax. (Fig. 36). — Tubercles present on 

 first abdominal segment. Gula triangular; pleurae nearly 

 contiguous behind its apex. (Fig. 25) 

 Goer in CE ( Fam . SericostomatidcE) . 



18b. Anterior angles of pronotum rounded. Head not retractile. 

 Four broad plates on mesothorax, but only two pairs of 

 smaller ones on metathorax. (Fig. 37.) No lateral 

 tubercles on first abdominal segment. Gula subquadrate; 

 pleurae separated widely by the gula. 

 BrachycentrincB (Fam. SericostomatidcE) . 



19a. Onlv lateral tubercles on first abdominal segment well 

 developed. Gills thread-like, single. Middle and hind 

 tibiae with one distal spur each. Prosternal horn present 

 Lepidostomatince (Fam. Sericostomatida) 



19b. All three tubercles on first abdominal segment well developed. 

 Gills thread-like, clustered; only on the anterior margins of 

 the segments. Middle and hind tibiae without distal spur. 

 No prosternal horn... Sericostomatina; (Fam. Sericostomatidce) 



Lake Forest College. 



