238 THE MARINE BOTANIST. 



tribe : with the exception of Bostrychia scorpioides, 

 it is the only member of the Rhodosperms which 

 gTows in fresh water and in its aspect it very nearly 

 resembles CaUithamnion Daviesii. 



GENERA OF THE CERAMIUM TRIBE. 



Ptilota, Frond compressed^ inarticulate, distich- 

 ous, pectinato-pinnate. Favellse stalked, invo- 

 lucrate. 



Microcladia, Frond filiform, inarticulate, dichoto- 



' mous. Favellae sessile. 



Ceramium, Frond filiform, articulate, dichoto- 

 mous. Tetraspores mostly immersed. 



Spyridia. Frond filiform, inarticulate, the branches 

 clothed with minute bristle-like, articulated ra- 

 muli. Tetraspores sessile on the ramuli. 



Griffithsia. Frond articulated, dichotomous, or 

 clothed with whorled, dichotomous ramuli, rose- 

 red. Favellse involucrated, sessile, or stalked. 

 Tetraspores sessile, on whorled ramuli. 



