Fig. ,^i. Invertebrate animals of a i6 square inch tniit on clav l)otlom, 

 Habitat No. Ixxi, Field No. 918. Isopods (Asclliis), the caddis-fly 

 Agraylca (upper left hand corner), and the mollusk Amnkola are 

 the principal animals present. Hyalella is abundant. 



