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. 1. Pleurot&nium. crenulalum (Ehrb.), an outline view, magnified ICO diameters. 

 Fig. 2. Pleurotcenium 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. Closterium lineatum (Ehrb.), an empty semicell, magnified 2CO 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 Brebissonii, Menegh., an empty frond, magnified 750 diameters and outline 

 of apex view. 



Fig. 7 a. Cosmarium tetropthalmum (Ktz.), outline of the empty frond, magnified 4GO diame- 

 ters. 



Fig. 8. Cosmarium margariliferum (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. 1 1. Micrasterias Jennerii, Ralfs, an empty semicell. 



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

 Fig. 12 a. Lateral view. 



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



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



Fig. 15. Micrasterias truncala, Corda, outline of front view, magnified 2CO diameters. 



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



Fig. 17. Staurastrum orbiculare, Ehrb., outline of the end view. 



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



Fig. 19. Staurastrum Lewisii, Wood, outline of the end view, magnified 750 diameters. 



Fig. 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 6. The end view with the same amplification. 



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



