262 EXPLANATION OF THE PLATES. 



Fig. 5. Outlines of Uuaatrum multilobatum, Wood. The lower figure represeuts a lateral view : 

 the upper a two-thirds view. 



Fig. C. Outline of Penium digitus, Breb. 



PLATE XXI. 



Fig. I. rieurotccnium crenulatuni (Ehrb.), an outline view, maguifieJ 100 diameters. 



Fig. 2. Pleurotccnium breve, Wood, the empty dead frond, raaguilied 750 diameters. 



Fig. 3. Tetmemorus Br&bissonii (Mengh.), an empty semicell. 

 Fig. 3 a. Outline of a whole irond. 



Fig. 4 b. Cloiiterium Unealum (Ehrb.), an empty semicell, magnified 200 diameters. 



Fig. 5. Cosmariinn Bolrytis (Bory), an empty frond, niagniiied 750 diameters. 

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



Fig. G. Cosmarium Brebissonii, Menegh., an empty frond, magnified 750 diameters and outline 

 of ape.\ view. 



Fig. 7 a. Cosmai-ium tetropthalmum (Ktz.), outline of the empty frond, magnified 4G0 diame- 

 ters. 



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

 ters; the outline of this should be more regular. 



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



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



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



Fig. 11. Micraslcrias Jcnncrii, Ralfs, an empty semicell. 



Fig. 12. Euaslrum ornalum, Wood, front view, magnified 450 diameters. 

 Fig. 12 a. Lateral view. 



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



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



Fig. 15. Micrasterias truncata, Corda, outline of front view, magnified 2C0 diameters. 



Fig. 10. Micrasterias cjranidala, Wood, front view of an empty frond, magnified 460 diameters. 



Fig. 17. Staurastrum orbicidare, Ehrb., outline of the cud view. 



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



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



Fig. 20. Staurastrum pa radoxicum, Mey., outline of end view. 



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

 Staurastrum paradoxum, Mcyen, 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. Siaurasti-um Pohjfrichum, Perty, outline of the frond as seen from the end. 



