EXPLANATION OF THE PLATES. 21 



PLATE XCL 



Fig. 1. Euastrum oblongum : a, front ; b, 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, dde ditto ; c 3 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 incisum. Fig. 9. Pediastrum heptactis. Fig. 10. Pe- 

 diastrum Napoleonis. 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. 

 1 6. Scenedesmus obtusus. Fig. 1 7. Cylindrocystis Brebissoni. 



PLATE XCIII. 



Fig. 1. Sph&rophora globulifera. Fig. 2. A portion of a 

 filament of Meloseira arenosa. 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. 

 Tetracyclus lacustris. Fig. 10. Bacillaria paradoxa. 



PLATE XCIV. 



Fig. 1. Diatoma vulgar e. Fig. 2. The same as in a more 

 advanced stage of its developement. Fig. 3. Diatoma 



