140 CONJUGATED. 



curious, and is confined to this and the following species. 

 The design of the interrupted conjugation is by no means 

 evident : it is remarkable, however, that the granules in those 

 cells, which remain disunited, decrease in size and become 

 almost colourless, while those of the conjoined cells increase 

 considerably, and darken in colour. This mode of conjugation 

 at least affords a decisive character by which it and the 

 following species may be known from all others hitherto de- 

 scribed. One fact is still wanting to complete the history of 

 tliis species, viz. the form of the sporangia, which might 

 possibly furnish an additional distinctive character. 



3. Zygnema intereuptum Hass. 



Plate XXL. 



Char. Filaments of considerable length, hut less in diameter 

 than those of Z. orhiculare. Cells at the j)eriod of conju- 

 gation rather longer than broad : previous to this, hoivever, 

 they are frequently not half so long as broad. Spires nu- 

 merous. Conjugation interrupted. Spire oval, equalling in 

 breadth the diameter of the cell but not producing any 

 inflation of it. 



Hassall, in Annals of Nat. Hist, vol, xi. p. 432. 



Hab. Cheshunt: A. H. H. 



This also is a very rare species. I have only met with it 

 once, but then in very considerable quantity. It bears a 

 close resemblance to Z. alternatum, but differs from it in 

 having filaments which are considerably smaller than those in 

 that species. The granules or unfertilized zoospores are like- 

 wise largest in those cells which have conjoined. 



4. Ztgnema serratum 7/as5. 



Plate XXIII. Figs. 1,2. 



Char. Filaments of nearly the same diameter as those of 

 Z. orhiculare, hut less mucous. Cells longer than broad. 

 Spires varying from three to five in number. Granules 

 larger. Conjugation continuous. Sporangia broadly 

 ovate. 



