40 Mr. H assail' s Notices of British Freshwater Conferva, 



Zygnema brevissimum. Cells scarcely so long as broad : a single 

 spiral tube performs one turn and a half within each cell ; 

 spores usually oval, but occasionally almost circular, their 

 long diameter being placed transversely in the cells. 

 This species comes very near to the Conjugata condensata 

 of Vaucher, who however represents the spores as being in that 

 species always of a perfectly circular form. Those cells, which 

 have not conjugated from some cause or other, frequently 

 swell up and assume a beaded form. 

 Vicinity of Cheshunt. 



Zygnema poly morphum. Filaments of less diameter than in 

 any of the preceding species ; cells at the period of conju- 

 gation about three times as long as broad : a single spiral 

 tube performs three or three and a half turns within each 

 cell ; spores not occasioning any inflation of the cells. 

 The above is the description of the species in its regular 

 form, from which, however, some of the filaments differ consi- 

 derably. Thus, in some, many of the cells which have not 

 conjugated are observed to have become inflated, and to present 

 a very characteristic appearance ; in others, in which the cells 

 are six times as long as broad, and which have not conju- 

 gated, spores completely formed, but of a very elongated shape, 

 are placed one within each cell, the inflation of which these 

 spores have not as yet occasioned: in a third set, which likewise 

 have not conjugated, the spores have become perfectly formed, 

 are much shorter, and now have produced considerable en- 

 largement of that part of the cells in which they lie ; and lastly, 

 in other filaments there is a regular alternate disposition of 

 spores and empty cells. 



This species comes very near to the Conjugata inflata of 

 Vaucher, in which, however, the spores are represented as 

 lying in inflated cells, which they do not in the species just 

 described. 



Vicinity of Cheshunt. 



Zygnema elongatum. Diameter of the filaments rather less 

 than in the preceding species ; cells very many times as long 

 as broad, down the interior of which a single tube passes 

 in a waved manner : at the situation of the joints, the appa- 

 ratus for the division of the threads, appearing like two 

 curved knife-blades, is situated. 



This is one of Vaucher's species, and a very abundant one 

 it is. It is mentioned by Mr. Dillwyn in his c Synopsis/ but 

 has been excluded from Harvey's ' Manual :' the grounds of 

 this exclusion I am not acquainted with. It is to be distin- 

 guished from Z. tenuissimum, on the one hand, by its longer 

 joints, laxness of the spiral tube, and greater diameter of the 



