REPORT OF THE DIRECTOR 1920-21 185 



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

 invertebrate species collected and reported and these have been tabu- 

 lated to show the distribution of the species from the sea (Labrador) 

 to the southernmost locality (Crown Point station) from which 

 they have been collected in the Champlain area. The total number 

 of Pleistocene species reported from all localities is 183. Of this 

 number, 89 have been collected from the vicinity of Montreal and 

 25 from Ottawa and vicinity. So far as reported, only 32 of the 

 total number of species entered the Champlain area, and of this 

 number 7 are listed without localities. At Port Kent, about 40 

 miles north of the Crown Point area, only 13 species occur; from 

 Burlington and vicinity, on the Vermont side, are reported 17 ( — ) 

 species. There is a rapid decrease in species from this point south- 

 ward : at Willsboro only 5 species occur (Saxicava rugosa, 

 Macoma groenlandica, Mytilus edulis, Yoldia 

 arctic a, Balanus crenatus); a few miles north of 

 Port Henry, 3 species (Macoma groenlandica, Saxi- 

 cava rugosa, Mytilus edulis); just north of Chimney 

 Point, Vt, 2 species (Macoma groenlandica, Yoldia 

 a r c t i c a) ; at Crown Point, 1 species (M acoma groen- 

 landica). 



By comparison of specimens of the Pleistocene species of the 

 Champlain area and Canada with recent representatives it has been 

 found that the Champlain fauna is a dwarf fauna, the dwarfed 

 character being well shown by 5 species : Macoma groen- 

 landica, Saxicava rugosa, Mytilus edulis, Mya 

 arenaria and Yoldia arctic a. In general, repre- 

 sentatives of all these species show a gradual decrease in size south- 

 ward. For example, in the case of Macoma groenlandica, 

 which extends farther south in the Champlain area than any other 

 species the largest shells from Crown Point are less than half the 

 size of the largest recent ones and less than three-fifths the size of 

 the largest shells from the Montreal area. The average Crown 

 Point shells are half, or less, the size of average recent shells and 

 three-fifths, or slightly over, the size of average Montreal specimens. 

 Another species, Cylichna alba, occurs in a dwarfed form 

 in the Champlain valley, but has only been found at Port Kent 

 and is there relatively infrequent. 



Just as it is found in the Baltic, so here, along with the dwarfing 

 of species goes a decreasing thickness of shell. This is seen best 

 in Cylichna alba, Yoldia arctic a, Macoma 

 groenlandica and Mya arenaria, but is also well 

 shown in Mytilus edulis and Saxicava rugosa. 



