I58 NEW YORK STATE MUSEUM 



species " in the North sea, of normal marine salinity, is the size 

 of a small apple; at Stockholm, where the salinity is below 10 permille, 

 the shell in the deeper, more saline water is only as large as a walnut 

 and is even smaller along shore where the water is fresher. At 

 Konigsberg, with the decreasing salinity, the size reaches that of 

 a hazelnut, whereas at Reval, it is only the size of a pea " (O'Connell, 

 p. 72). The studies made of the Baltic sea have shown that the 

 fauna of a brackish-water body of the nature of the Baltic is due 

 to a mingling of marine species and fresh-water (river) species which, 

 however, are modified. Only the most euryhaline marine species 

 survive. A very important fact brought out is that, however 

 dwarfed or otherwise modified the species may be, the marine forms 

 of the Baltic are not different specifically from those living in water 

 of normal marine salinity nor do the fresh-water forms differ speci- 

 fically from those found in the rivers emptying into the Baltic 

 or those in nearby fresh-water bodies (Forbes, p. go; Pouchet & 

 de Guerne, p. 920, 921). 



Examples of dwarfing due to freshening of sea water have been 

 noted elsewhere than in the Baltic. Cardium edule, 

 which is common along the British coast, is found in a dwarfed 

 condition in the brackish waters of the estuaries. The shell is 

 invariably reduced in size, and in addition is thin and with less 

 strongly marked external characters. The cockle of the Greenland 

 estuaries is likewise thin, smooth and almost edentulous; in each 

 valve of the young shells are found rudiments of a single tooth 

 which finally disappear. This species of Cardium is very 

 abundant in the Pliocene (Crag) of Suffolk and Norfolk, but is 

 not now found in Europe (Forbes, p. 213-14; see Shimer, p. 474). 



Both the Caspian and Black seas have fresher water than the 

 Atlantic ocean, due to the many streams emptying into them. The 

 fauna in each case is typically marine and the species are the same 

 as those in the Atlantic, but in these seas they are practically all 

 dwarfed in size as compared to the Atlantic specimens. Ten species 

 of Cardium are found in the Caspian sea, small, thin, with 

 lateral or central teeth or both suppressed. Often one tooth alone 

 is preserved; at times it acquires a great development and is accom- 

 panied by great distortion of the shell on that side. These are 

 all aberrant forms, all related back to Cardium edule. The 

 same is true of the cockles of the Black sea (Forbes, p. 201-2, 211-15 ; 

 see Shimer, p. 473, 474). Among other species dwarfed by brackish 

 water are Mya are n aria and Littorina littorea. 



