144 CONJUGATED. 



usually four in number. Sporangia circular, lodged in cells, 

 which are considerably enlarged for their accommodation. 



Z. pellucidum Hassall, in Ann. Nat. Hist. vol. x. p. 37. 

 Hal. Cheshunt: A. H. H. 



This is a very curious and beautiful species, and one by 

 no means common. I have only once been so fortunate as to 

 meet with it in a state of reproduction, in which condition it is 

 not possible to confound it with any other described species. 



10. ZYGNEMA RIVULARE Hass. 

 Plate XXVII. Figs. 1, 2. 



Char. Filaments seven or eight inches in length, usually at- 

 tached, and in diameter about equal to those of Z. pellu- 

 cidum. Cells varying in length from four to eight times 

 their diameter. Spires serrated, three or four in number. 

 Granules large. 



Z. rivulare Hassall, in Annals of Nat. Hist. vol. x. p. 38. 

 Dill, t, 4. A. B. 



Hob. In the Barge, New, and Lea rivers, near Cheshunt, 

 abundant : A. H. H. Cader Idris : Mr. Ralfs. 



This is a very distinct species, and certainly not the 

 Conjugata adnata of Vaucher, the filaments of which equal 

 nearly those of Z. nitidum in diameter. I have never been 

 so fortunate as to find it in a state of reproduction. It would 

 not appear to be common, as I have not received it from any 

 other of my correspondents save Mr. Ralfs. 



b. Spires two in number in each cell. 



11. ZYGNEMA DECIMINUM Ag. 

 Plate XXIII. Figs. 3, 4. 



Char. Filaments rather smaller than those of Z. neglcctnm. 

 Cells twice or thrice as long as broad. Spires two, crossing 

 each other. Granules large. Sporangia oval, obtuse, not 

 producing inflation of the cells in which they are lodged. 



