Mr. Hassall's Notices of British Freshwater Conferva. 37 



cerned winding round the interior of the cells : these con- 

 tain the reproductive globules, which are large and distinct, 

 with a dark central nucleus ; cells in the young filaments 

 scarcely so long as broad, but rather longer than broad in 

 those which have conjugated. Seeds oval, sometimes almost 

 circular, lying in inflated ceils, the cavity of which they do 

 not fill. 



This well-marked species has occurred to me in several lo- 

 calities in the vicinity of Cheshunt, in one of which, viz. in 

 two sheltered ponds, communicating with each other by a nar- 

 row channel, opposite to Sir Henry Meux's house, it is very 

 abundant — not floating upon the surface, but diffusing itself 

 through the water, to which it imparts a rich emerald green 

 colour. The diameter of the filaments is little less consider- 

 able than that of Z. nitidum, whose equal, if not superior in 

 beauty, this fine species may be fairly considered. 



Zygnema quadrispirale ? Filaments of somewhat less diameter 

 than those of Zygnema nitidum ; cells from three to five 

 times as long as broad ; winding round the interior of 

 these are spiral tubes, usually four in number. 



Zygnema neglectum. Filaments of considerable diameter and 

 length ; cells rather longer than broad, lining the interior 

 of which are spiral tubes, usually three in number, which 

 in the young filaments perform collectively within each cell 

 about six revolutions, but in the more aged filaments a 

 smaller number. Spores occasioning no inflation of the cells. 

 I should have but little hesitation in referring this species 

 to the Conjugata adnata of Vaucher ; but abundant as it is, and 

 frequently as I have observed it, I have never met with it at- 

 tached to any object, but invariably free and floating, some- 

 times unmixed with any other species, but more frequently 

 entangled among the filaments of Z. nitidum and Z. quininum. 

 It is for this reason therefore that I hesitate to regard it as 

 identical with that species. The filaments are intermediate 

 in diameter between that of Zygnema nitidum and Z. decimi- 

 num, to both of which it bears outwardly some resemblance. 

 The number of spiral tubes varies, but is usually three ; while 

 in Zygnema nitidum the prevailing number is four, and in Z. 

 deciminum but two. 



Abundant in the neighbourhood of Cheshunt. 



Zygnema pellucidum. Filaments of more considerable diameter 

 than those of Zygnema rivulare ; cells usually seven or eight 

 times as long as broad, never less than five, and frequently 

 as many as ten times : four faint spires scarcely at all visi- 



