6 BULLETIN" 15 8, UNITED STATES NATIONAL MUSEUM 



areas possess the same salinity and mineral contents; ponds into 

 whose inland ends run streams of fresh water large enough to be 

 called rivers, while the other ends open directly into the ocean ; ponds 

 virtually large tide pools, into which the tide flows and ebbs twice a 

 day, and during a longer or shorter interval remains at the same 

 level; ponds filled with fresh water the greater portion of the year, 

 but into which the neap tides pour salt water every spring and fall ; 

 ponds whose bottoms are composed of mud so soft that it is impossi- 

 ble to wade in them ; ponds with bottoms of hard sand and gravel ; 

 and ponds whose bottoms are continuous ledges of solid rock. 



The same variety of ponds is found around the shores of Marthas 

 Vineyard, Chappaquiddick Island, and Nantucket. The largest of 

 these ponds on Marthas Vineyard is called Edgartown Great Pond. 

 From its inland end is pumped Edgartown's supply of drinking 

 water, while the outer end periodically opens into the Atlantic. 



Away from the shores of Cape Cod and the islands is another 

 series of ponds, all of which are filled with strictly fresh water. 

 These are of glacial origin and show a similar variation in size, in 

 the quantity of vegetation they contain, and in the kind of bottom. 



Under such diverse conditions it would naturally be expected that 

 the plankton would vary greatly, and such we find to be the case. 

 The faunas of these ponds are almost entirely made up of species 

 unlike those of the neighboring ocean, and no two of the lists are 

 alike. As a result these ponds have contributed a very large num- 

 ber of species new to the region and several species new to science. 

 (See Appendix A, p. .534, for list and description of the ponds of 

 the area.) 



SAND BEACHES OF THE AREA 



At first the idea of sand as a habitat for copepods seems absurd, 

 but from the very beginning of plankton investigation it has been 

 known that many copepods persistently remain on or near the bot- 

 tom. Other species are known to inhabit marine algae, and still 

 others habitually live on fresh-water mosses and aquatic plants. 

 Recently it has been discovered that a few forms live in the damp 

 moss of deep forests, away from any actual body of water. 



It may now be added that a great variety of copepods select for 

 their habitat the sands of the bathing beaches, offshore banks, and 

 fresh-water lakes and ponds. Even those exposed shores where the 

 surf pounds the hardest and the most continuously yield a surprising 

 copepod fauna. If the sand from such localities, where it is cov- 

 ered by water, be scraped up to a depth of 2 or 3 inches and 

 thoroughly washed, the wash water will be found to contain a re- 

 markable number and variety of copepods. This is true between 

 tide marks as well as just beyond low-water mark when the tide is 



