REPORT OF THE DIRECTOR I92O-2I 1 59 



In general, species that live in both normal sea water and 

 in brackish water are smaller in the latter. There are some excep- 

 tions to this (Forbes, p. 230; see Shimer, p. 474), as, for example, 

 Scrobularia and Mactra solida. These forms have 

 become thoroughly adapted to a brackish water environment, 

 and, moreover, attain their largest size there. 



Modifications due to changes in the salt content of water are 

 not confined to invertebrates alone; and while this paper is con- 

 cerned with invertebrate species only, it is not amiss here to point 

 out a case or two in which a higher group, the fishes,. are affected. 

 The dwarfing of fishes in the Baltic has been noted above. Forbes 

 (p. 204) shows that the fishes of the Black sea are very indicative 

 of the estuarine character of its waters. The number of species is 

 remarkably small when compared with those of the Mediterranean ; 

 but on the other hand the number of individuals is marvelously 

 great. Lull (p. 172) points out ontogenetic variation dependent upon 

 the chemical content of the water in little fishes known as stickle- 

 backs (Gasterosteus cataphractus). " Those living 

 in salt water have from twenty to thirty bony plates along the back, 

 in brackish water these are reduced to from fifteen to three, while 

 in fresh water there are none at all." 



Pleistocene Fossils of the Champlain Sea 



Part 1 Decrease in Species Southward 



A careful list, with localities, has been compiled of the marine 

 Pleistocene invertebrate species collected by the writer and also 

 all those reported by others in various publications; and these have 

 been tabulated to show the distribution of the species from Labrador 

 to the southernmost locality from which they have been collected 

 in the Pleistocene of the Champlain valley. 



