470 
MOLLUSKS. 
FLUVIATILE SPECIES. 
Physa gyrina. Very common. 
Lymnea reflexa. Rare. 
- LAND SPECIES. 
Agriolimax campestris. Common. 
The absence of Spheriude is noteworthy. 
INSECTS, 
Hydroporus undulatus Diving Beetle. 
Dytiscus sp. Larva of water-beetle. 
Notonecta undulata. Back-swimmer. 
Corixa interrupta. Water-boatman. 
Limmotrechus marginatus. Water-strider. 
Leucorhinia sp. Dragonfly (nymph). 
Libellula basalis. Dragonfly (adult). 
Epieschna heros. Dragonfly (nymph). 
CRUSTACEA. 
Cambarus blandingt acutus. Crawfish. 
STATION XIX, 
An irregular depression, two hundred or more feet west of 
Station XVII, lying in a northeast by southwest direction. This 
area is about one hundred feet long by forty feet wide, and is well 
stocked with plant life, among which the following species are con- 
spicuous: 
Iris versicolor. Large Blue Flag. 
Sparganium eurycarpum. Broad-fruited Bur-Reed. 
The following species of trees surround the area: 
Ostrya virginiana. Hop Hornbeam. 
Crategus punctata. Large-fruited Thorn. 
Carya ovata. Shellbark Hickory. 
Quercus bicolor. Swamp White Oak. 
Cephalanthus occidentalis. Button-bush. 
During the spring this depression is filled with water to the 
depth of about eighteen inches. In the summer the water evapo- 
rates and the ground becomes hard and sun-baked. The mollusks 
