262 EXPLANATION OF THE PLATES. 



Fig. 5. Outlines of Euastrum multilobatum, Wood. The lower figure represents a lateral view ; 

 the upper a two-thirds view. 



Fig. 6. Outline of Penium digitus, Breb. 



PLATE XXI. 



Fig. L Pleurotoenium crenulatum (Ehrb.), an outline view, magnified 160 diameters. 



Fig. 2. Pleurotoenium breve, Wood, the empty dead frond, magnified 750 diameters. 



Fig. 3. Tetmemorus Brebissonii (Mengh.), an empty semicell. 

 Fig. 3 a. Outline of a whole frond. 



Fig. 4 b. Glosterium lineatum (Ehrb.), an empty semicell, magnified 260 diameters. 



Fig. 5. Cosmarium Botrytis (Bory), an empty frond, magnified 750 diameters. 

 Figs. 5 a and 5 b. Outlines of semicells to show the variety of form. 



Fig. 6. Cosmarium Bribissonii, Menegh., an empty frond, magnified 750 diameters and outline 

 of apex view. 



Fig. 7 a. Cosmarium tetropthalmum (Ktz.), outline of the empty frond, magnified 460 diame- 

 ters. 



Fig. 8. Cosmarium margaritiferum (Turp.), view of an empty semicell, magnified 750 diame- 

 ters; the outline of this should be more regular. 



Fig. 9. Cosmarium suborbiculare, Wood, an empty frond, magnified 750 diameters. 



Fig. 9 a. An outline of end view of similar amplification. 



Fig. 10. Cosmarium Broomei, Thw., lateral outline of the frond. 



Fig. 11. Micrasterias Jennerii, Ralfs, an empty semicell. 



Fig. 12. Euastrum ornatum. Wood, front view, magnified 450 diameters. 

 Fig. 12 a. Lateral view. 



Fig. 13. Euastrum Didelta, Turpin, outline of the front view. 



Pig. 14. Euastrum elegans, Breb., outline of the lateral view, 



Fig. 15. Micrasterias truncata, Corda, outline of front view, magnified 260 diameters. 



Fig. 16. Micrasterias granidata, Wood, front view of an empty frond, magnified 460 diameters. 



Pig. 17. Siaurastrum orbiculare, Ehrb., outline of the end view. 



Fig. 18. Staurastrum, dejectum, Breb., outline of the end view, magnified 750 diameters. 



Pig!* 19. Staurastrum Lewisii, Wood, outline of the end view, magnified 750 diameters. 



Pig. 20. Staurastrum paradoxicum, Mey., outline of end view. 



Fig. 21. The five radiate figure is an end view of Staurastrum Arachne, Ralfs, the triradiate of 

 Staurastrum paradoxum, Meyen, magnified 750 diameters. 



Fig. 22. Staurastrum Ravenellii, Wood, Front view of the empty frond, magnified 460 diameters 

 Fig. 22 a. The side view of an empty semicell, magnified 750 diameters. 

 Fig. 22 b. The end view with the same amplification. 



Fig. 23. Staurastrum Polytrichum, Perty, outline of the frond as seen from the end. 



