EXPLANATION OF THE PLATES. 21 



PLATE XCI. 



Fig. 1. Euastrum oblongum : a, front ; Z>, side views ; c, empty 

 frond. — Fig. 2. Euastrum insigne. — Fig. 3. Euastrum 

 Pelta : a, front ; b, side view ; c, empty frond. — Fig. 4. 

 Euastrum binale. — Fig. 5. Variety of same. — Fig. 6. 

 Euastrum gemmatum : a, front view ; b, side ditto ; c, d, 

 end view ; e, variety. — Fig. 7. Euastrum verrucosum : a, 

 front view of young frond ; b, ditto of adult frond ; c, side 

 view ; d, end view. — Fig. 8. Euastrum rostratum. — Fig. 9. 

 Euastrum spinosum : a, b, d, e, f, front view, and showing 

 the mode of formation of new fronds ; c, end view. — 

 Fig. 10. Euastrum. — Fig. 11. Euastrum Didelta: a, front 

 view ; b, transverse ; c, d, end views. 



PLATE XCII. 



Fig. 1. Pediastrum tricyclium. — Fig. 2. Pediastrum ellipticum. 

 — Fig. 3. Pediastrum lunar e. — Fig. 4. Pediastrum cribri- 

 forme. — Fig. 5. Pediastrum hexactis. — Fig. 6. Pediastrum 

 excavatum. — Fig. 7. Pediastrum Rotula. — Fig. 8. Pedias- 

 trum i?icisum. — Fig. 9. Pediastrum heptactis. — Fig. 10. Pe- 

 diastrum Najooleonis. — Fig. 11. Pediastrum Napoleonis var. 



— Fig. 12. Scenedesmus quadricaudatus : a, frond in its or- 

 dinary state ; b, var. with three spines ; c, var. destitute of 

 spines. — Fig. 13. Scenedesmus dimorphus. — Fig. 14. Scene- 

 desmus acutus. — Fig. 15. Scenedesmus triseriatus. — Fig. 

 16. Scenedesmus obtusus. — Fig. 17. Cylindrocystis Brebissoni. 



PLATE XCIII. 



Fig. 1. Spharophora globidifera. — Fig. 2. A portion of a 

 filament of Meloseira arcnosa. Fig. 3. End view of a 

 frustule of the same. — Figs. 4 and 5. Meloseira varians. 



— Figs. 6 and 7. Meloseira orichalcea. — Figs. 8 and 9. 

 Tetracyclics lacustris. — Fig. 1 0. Bacillaria paradoxa. 



PLATE XCIV. 



Fig. 1. Diatoma vulgare. Fig. 2. The same as in a more 

 advanced stage of its developcment. — Fig. 3. Diatoma 



