24 



Fresh-water Biology 



{Continued from page 22) 



20 — Antennas as long as half the body; sixth abdominal segment of the male roundly 



emarginate Limnoporus 



— Antennae not as long as half the entire length of the insect, not extending beyond the 

 thorax; sixth abdominal segment of male doubly emarginate Gerris 



21 — First antennal segment much shorter than the other three taken together; not much 



longer than the second and third taken together, and sometimes shorter 22 



— First antennal segment nearly equal to the remaining three taken together, much 

 longer than second and third; antennas almost as long as entire bod}-; hind femora 

 twice as long as hind tibia Metrobates 



22 — Fourth (apical) segment of antennae longer than the third Trepobates 



— Fourth segment of antennas never more than equal to third; basal segment of anterior 

 tarsi much shorter than second; hind femur equal to or much shorter than hind 

 tibia and tarsus taken together Rheumatobates 



23 — Last antennal segment longest 24 



— First antennal segment longest 25 



24 — Ocelli in contact with inner margin of the e3'es Macrovelia 



— Ocelli absent Microvelia 



25 — Third segment of middle tarsus split and with feathery hairs set in the split. Rhagovella 

 — Intermediate tarsi not split Velia 



KEY TO GENERA OF CADDIS WORMS: TRICHOPTERA 



1 — Microcaddis fly larvae: length less than 6 mm.: abdomen wider than thorax: case 

 shaped like a spectacle case and generally carried edge upward: usually no gills. 

 Hydroptilidae (Not included in plate or table. Several genera.) 



— Large caddis flies: abdomen of larva hardly wider than thorax 2 



2 — Caudal prolegs separate: no portable cases (except Glossosoma) 3 



— Caudal prolegs fused on middle line to form an apparent tenth segment 9 



3 — Case turtle shaped, its opening below Glossosoma 



— Case not so 4 



4— Gills present: net-spinners Hydropsyche 



— Gills absent 5 



5 — Free, living under stones : color green : seg. 9, chitinized above Rhyacophila 



— Living in tubes: abdominal segment 9 not chitinized above 6 



6 — In firm tubes in bottom mud Phylocentropus 



— In filmy tubes below stones or among weeds 7 



7 — In J-shaped tubes Neurecllpsis 



— In straight tubes 8 



{Continued on page 26) 



♦ See plate 13 for the worms themselves. Figures 2 to 15 are from Dr. J. T. Lloyd. 



