Plate VII; Figures 50 to 56; All except Fig. 54a Magni- 

 fied 1000 Diameters. 



Fig. 50. Pediastrum pertusum var. clathratum 

 A. Br 



Fig. 51. Coelastrum microporum Nag'. 



Fig. 52. Pediastrum pertusum var. clathratum 

 A. Br 



Fig. 53. Characium Naegelii A. Br. 



Fig. 54. Kirchneriella obesa (West) Schmidle. 

 Fig. 54a represents a single cell 



Fig. 55. Sorastrum spinulosum Nag. 



Fig. 56. Characium ambiguum Herm. . 



