ART. 15 COPEPOD CRUSTACEANS OF CHESAPEAKE BAY WILSON 9 



at Station U was only 11 meters, but the bottom salinity was about 

 three times that at the surface. If these species migrate daily up 

 and down as they are known to do elsewhere, the change in salinity 

 must be more or less abrupt in so short a distance. 



2. The 10 copepods found exclusively or most abundantly in the 

 inner bay may be regarded as brackish-water species, since they were 

 found in water with an average salinity of 15 per cent or less. They 

 also are probably able to accommodate themselves to rapid changes 

 in salinity, especially to those involving reduction. 



3. The 16 species found exclusively in the outer bay may be re- 

 garded as salt-water forms. They were found in water with a salin- 

 ity ranging between 20 and 30 per cent, and the changes are not so 

 great as for the other two groups. 



4. The 14 species confined to single areas in the bay will be con- 

 sidered separately, since salinity may have been one of the factors 

 determining their distribution. Table 2 gives the complete statis- 

 tics with reference to these species and will serve for the other 

 aspects of distribution as well as for that of salinity. 



The Cletodes species has been recorded from various European 

 localities, all of which were considerably farther north. No record 

 of the salinity of the water in which the specimens were found has 

 been given, but judging from the localities it seems probable that it 

 was higher than that here recorded. The single species of each of 

 the genera Corycdeus^ Corycella^ Diogaccus, Harpacticus^ and Oitho- 

 na, together with the new species of Pontella, were all taken in water 

 of normally high salinity, between 25 and 30 per cent. Giesbrecht 

 described four species of Cryptopontius from the Bay of Naples, 

 and Sars reported one of them from the south coast of Norway. 

 They were all bottom forms, but nothing was said about the salinity 

 of the water in which they were found. The new species here 

 recorded comes also from the bottom at one of the deepest stations 

 near the mouth of the bay, where the salinity is fairly high. 

 Ectinoso7na normani was first recorded from the Firth of Forth in 

 Scotland and afterwards from Vadso, Finmark, and the upper part 

 of the Christiania Fiord in Norway, from a depth of 6 fathoms on a 

 muddy bottom. The present specimens came from near the inner 

 end of the bay, at about twice the depth (20 meters) on a muddy 

 bottom where the salinity was low. The Lahidocera species has 

 been reported by Giesbrecht from the Atlantic Ocean between lati- 

 tude 36° and 55° N. The mouth of the bay where the present speci- 

 mens were obtained is on the parallel of latitude 37° N., and the 

 salinity is but little less than that of the open ocean. Metacyclops 

 is a fresh-water copepod, found in lakes and rivers all over the world. 

 Here it was obtained just below the mouth of the Patapsco Kiver, 

 79858—32 2 



