ZYGNEMA. 141 



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



Hob. Cheshunt, very rare : A. H. H. Withy ham : Mr. 

 Jenner. 



The only species with which this can possibly be confounded 

 is Z. orliculare, from which it may be readily distinguished by 

 the fewer number and serrated appearance of the spires, the 

 larger size of the granules, and the form of the sporangia, 

 which in Z. orliculare are nearly spherical, and compressed, 

 while in Z. serratum they are broadly ovate. The filaments 

 do indeed resemble very closely in character those of Z. niti- 

 dum, with which, however, there is but little danger of con- 

 founding it, that species being altogether a much smaller plant. 

 It is very rare. 



5. ZYGNEMA NITIDUM Ag. 

 Plate XXII. Figs. 1, 2. 



Char. Filaments of much less diameter than those of Z. serra- 

 tum. Cells usually rather more than twice as long as broad. 

 Spires generally four in number. Granules large. Spo- 

 rangia acutely ovate. 



Conferva jugalis Miiller, Flora Danica. Conjugata princeps 

 Vaucher, Hist, des Conf. d'Eau douce, p. 64. pi. iv. fig. 1 . 

 F. nitidum Harv. in Manual, p. 143. ; Agardh's Sy sterna. 

 Conf. nitidum Dillwyn, British Confervse, pi. iv. f. c. ; 

 Eng. Bot. t. 1656, in part. 



Hoib. Every where common throughout Great Britain 

 and Ireland. 



This species is one of the best marked as well as most 

 beautiful of the tribe. Numerous other Zygnemata have 

 however doubtless been associated with it under the same 

 name. 



Vaucher has the following observation upon it : ( < Inde- 

 pendently of its size, it is distinguished from all others by a 

 coarser touch, a more shining appearance of tubes almost crisp, 

 and by its constant habit of raising its extremities out of 

 the water whenever it is immersed in the liquid." 



