Plate IV. 
Fig. la, 1b.—Hyalotheca hians, Nordst. 
Fig. 2a, 2c, 2d.—Cosmarium amplum, Wordst, 
Fig, 3a, 3b, 3c.—Cosmarium minutum, Delp. 
Fig. 4.—Cosmarium crenatum, 
Fig. 5.—Cosmarium Portianum. 
Fig. 6, 7.—Micrasterias incisa, var. Wallichiana. 
Fig. 8, 9.—Micrasterias incisa, var. typica. 
Fig. 10,—Cosmarium, 
