June, 1919] 



Fauna of Rock Bottom Ponds 



433 



water had, in turn, the next greatest number of inhabitants. 

 The bottom and pelagic habitats had the fewest forms. The 

 relative positions of the old and the young PhyscB and also of the 

 nymphal and adult Notonecta are interesting. As indicated in 

 the table the young PhyscB were almost exclusively on the 

 filamentous algae suspended in the water. On the other hand 

 the older and larger individuals were chiefly on the semi-mucky 

 material beneath the algae. The nymphs of Notonecta were 

 likewise in the algae. They were most numerous in some which 

 rested on a ledge about six inches below the surface. The leech, 

 Glossiphonia stagnalis, was particularly abundant on Char a. 



Station 2 of Pond I. 



The gyrinid beetles were unusually numerous; one hundred 

 of them were counted in a strip three inches wide and five 

 feet long. In a strip five feet wide and one hundred feet long I 

 estimated that there were 3,000. Most of those within the 

 area covered by Station 1 were collected in this strip. It was 

 noticeable that the beetles were not abundant over the main 

 portion of the pond beyond the shelter afforded from strong 

 breezes by the high walls enclosing the station. 



Station 2. The section of the quarry included in this 

 station was not covered with water until within less than a year 

 of the time it was studied. It is interesting because it was 

 within 250 feet of Station 1, parts of which had been inter- 



