20 EXPLANATION OF THE PLATES. 



Fig. 18. Pediastrum simplex. Fig. 19. Pedia strum ele- 

 gans. 



PLATE LXXXYII. 



Fig. 1. Closterium Ehrenbergii* Fig. 2. Closterium monili- 

 ferum. Fig. 3. Closterium turgidum. Fig. 4. Closterium 

 striolatum. Fig. 5. Closterium acerosum. Fig. 6. Clos- 

 terium rostratum. Fig. 7. Closterium setaceum. 



PLATE LXXXVIH. 



Fig. 1. Closterium lineatum. Fig. 2. Closterium Cornu. 

 Fig. 3. Closterium Trabecula. Fig. 4. Closterium Digi- 

 tus. Fig. 5. Closterium margaritaceum. 



PLATE LXXXTX. 



Fig. 1. Xanthidium furcatum. Fig. 2. Xanthidium fascicu- 

 latum f Fig. 3. Xanthidium aculeatum : a, front view ; b, 

 end view ; e, side view ; d, new segment. Fig. 4. Xan- 

 thidium polygonum. Fig. 6. Tetmemorus granulatus : a, 

 front view ; b, side view ; c, empty frond ; d, fronds con- 

 jugated, showing mode of formation of the sporangium ; e, 

 sporangium perfectly formed. Fig. 5. Tetmemorus Bre- 

 bissoni : a, front view ; b, side view ; c, empty frond ; d, 

 segment of frond. 



PLATE XC. 



Fig. 1. Micrasteruisrotata: a, adult frond ; b, c, young fronds 

 of same; d, showing the mode of formation of the new 

 segment. Fig. 2. Micrasterias radiata. Fig. 3. Holo- 

 , cystis oscitans ? (Euastrum crux meUtensis, young, Ehr.) 

 Fig. 4. Holocystis oscitans. Fig. 5. Euastrum circulare. 

 Fig. 6. Euastrum. Fig. 7. Micrasterias crux meUtensis 

 (Euastrum crux meUtensis Ehr.). Fig. 8. Euastrum Di- 

 delta : a, front ; b, side view. Fig. 9. Euastrum affine; a, 

 front ; by side view. Fig. 10. Euastrum, 



