NOTE. 



Figures 1 to 6, Plate XI, are twice the size of the shell. 

 " 7 to 25, Plate XI, are six times the size of the shell. 

 " 1 to 25, " XII, " " " " 



ERRATA. 



Species No. 8, Pisidium tenellum, p. 358, line 11, is represented by Plate 

 XI, figures 22 and 23 only. 



Species No. 11, P. minus, p. 360, line 17, is represented by Plate XII, 

 figures 2, 3, 4, instead of 5, 6, 7. 



