148 CONJUGATED. 



species from those of Z. commune before conjugation : after 

 this has occurred, the difference in the length of the cells and 

 the form of these is so obvious as not to leave any doubt of 

 its being distinct from that species. To this species ought, I 

 think, the Zygnema brevissimum, described by me in vol. x. 

 p. 40. of the " Annals of Nat. Hist." to be referred. I am still 

 not sure, however, but that it is distinct, yet fear to regard it 

 as such. The cells in it are scarcely so long as broad ; the 

 sporangia broadly oval, sometimes almost circular, their long 

 diameter being placed transversely in the cells, which are 

 frequently highly inflated. 



17. ZYGNEMA COMMUNE Hass. 

 Plate XXVIII. Figs. 5, 6. 



Char. Filaments about equal in diameter to those of Z. cate- 

 naforme. Cells usually three times as long as broad. Spo- 

 rangia acutely oval, not occasioning any inflation of the 

 cells in which tliey are formed. 



Zygnema commune Hassall, in Annals of Nat. Hist. vol. x. 

 p. 39. ; Dillw. t. 3. upper figure, in part ? 



Hab. Cheshunt : A. H. H. Framfield Common : Mr. 

 Jenner. Parkind Quarry : Major Martin. 



This is a very distinct and regular species. 



18. ZYGNEMA GRACILE Hass. 

 Plate XXX. Figs. 5, 6. 



Char. Filaments of less diameter than those of Z. commune. 

 Cells usually four times as long as broad, and inflated on 

 the side which gives origin to the tubes of communication. 

 Sporangia acutely oval, not rendering the cells at all ven- 

 tricose. 



Hab. Wanstead Flats, Essex ; Cheshunt : A. H. H. 



Apparently a distinct species, known from Z. commune by 

 the smaller size of the filaments and lateral enlargements of 

 the cells. 



