DESMIDIUM. 345 



therefore been induced to institute a new genus for D. 

 cylindricum, under the name of Didymoprium. This genus, 

 in my humble opinion, ought not to be adopted ; and if it be 

 really a good and valid genus, then is there sufficient reason 

 why D. Borreri should form the type of a genus different 

 from both, for it differs from D. Swartzii in the cells being 

 biangular and not triangular, and from Desmidium cylindricum 

 Grev., the Didymoprium Grevillei of Kiitzing, in the absence 

 of a mucous sheath. There would thus be as many genera as 

 there were formerly considered to be species of Desmidia, a 

 result not altogether satisfactory. 



c. Filaments with four angles. 



4. DESMIDIUM QUADRANGULATUM Rolfs. 



Plate LXXXIV. Fig. 3. 



Char. Filaments quadrangular. J^ndochrome four-rayed. 

 Ralfs, in Annals, vol. xv. p. 405. pi. xii. fig. 9. 



Hob. In a boggy pool at Balogas, near Penzance : Mr. 

 Ralfs. 



Notwithstanding the strong resemblance which it bears to 

 Desmidium Swartzii, this plant appears to me to be very dis- 

 tinct. In consequence of the filaments having four angles 

 instead of three, and as they are spirally twisted in the 

 same manner as those of other Desmidia, it follows, that two 

 dark, and waved lines, describing two of the four angles, are 

 visible in the length of the thread. The observation of these 

 will at once serve to distinguish it from Desmidium Swartzii, 

 of which Mr. Berkeley, Mr. Borrer, and Mr. Ralfs consider 

 this plant to be a variety : the latter, however, remarks 

 that he has gathered it for two successive years quite unmixed 

 with that species. 



It seems to me that this plant has not merely a right to be 

 considered as specifically distinct from D. Swartzii, but nearly 

 as much claim (a claim however which I do not allow) to be 



