June, 1919] 



Fauna of Rock Bottom Ponds 



443 



the deepest having only five inches of water. A very shght 

 change in the pond would obviously have wrought a great 

 change in the pools. Unless otherwise indicated the conditions 

 to be described will apply only to those pools directly connected 

 with the pond. 



The bottom was covered with pebbles, sand and chips of 

 stone. The larger vegetation consisted chiefly of willow shoots. 

 On the ridges between pools there was a miscellaneous scattering 

 of grasses and weeds. Within the pools there were abundant 

 growths of filamentous algse. 



Station 2 of Pond II. 



Table 8, page 444, includes the forms from three pools. The 

 species marked with an asterisk were all found in a pool broadly 

 joined with the pond. Not all of these were in the other two 

 pools. 



Two-thirds of the snails were on the upper side of small 

 stones. Most of them were young. They were far more abun- 

 dant where algae grew than they were on a bare substratum. In 

 one pool containing algae there were fifty-five PhyscE in an area 

 twelve by eighteen inches, whereas in a pool with practically 

 no algae there were only forty-five of them in an area seven feet 

 by eighteen inches. Chironomid larvae were present in great 

 numbers. The Odonata were found near the edge of the pool 

 among pebbles and sand. 



