Mylilus edulis Linn. 



Fig. i Recent specimen (left valve) from Cape May, N. J. 



Fig. 2 Outlines of left valves showing comparison in size of the largest Pleisto- 

 cene specimens from localities in New York with one of the largest recent 

 specimens, a, recent, Cape May, N. J.; b, Lapham Corners; c, Port Kent. 



Fig. 3 Similar outlines of average-sized specimens, a, recent New York coast; 



b, recent, Gay Head, Martha's Vineyard, Mass.; c, Lapham Corners; d, Port 

 Kent (Willsboro about the same). 



Yoldia arctica Gray 



Fig. 4 Right valve of a large-sized recent specimen. 



Fig. 5 Outlines of right valves showing comparison in size of the largest 

 Pleistocene specimens from localities in Canada and New York with one of 

 the largest recent specimens, a, recent; b, Montreal; c, Ottawa; d, Burlington; 

 e, Port Kent; /, Willsboro; g, Chimney Point. 



Fig. 6 Similar outlines of medium-sized valves, a, recent; b, Canada 

 (Montreal); c, Port Kent; d, Port Kent (majority of specimens). Port Kent 

 material is taken as typical of the Champlain specimens, because there are larger 

 numbers to judge from. 



Fig. 7 Outline of right valves showing variation in shape of Pleistocene speci- 

 mens, a, Ottawa; b, c, d, Port Kent, a and d represent the two extremes. 



Cylichna alba Brown 

 Fig. 8 Pleistocene specimen from Canada (Dawson, Can. Ice Age, p. 244). 

 Fig. 9 Outlines showing comparison in size of Canadian and Port Kent speci- 

 mens, a, Canadian specimen; b, one of the largest Port Kent specimens; 



c, specimen representing the size of the majority of Port Kent forms. 



