432 Mr. Hassall's Notices of British Freshwater Confervce. 



In most species of Conjugata, at the period of reproduction, a 

 number of contiguous cells of one filament unite with the op- 

 posed cells of another filament, but the arrangement is differ- 

 ent in specimens of this species in its ordinary state ; in these 

 it is usually only every second or third pair of cells which 

 conjugate, and as soon as this conjugation is about to take 

 place a very curious phenomenon occurs : the spherical gra- 

 nules contained within the spiral coil of the pair of cells which 

 have united increase in size and deepen in colour, while at the 

 same time those contained in the intermediate cells which 

 have not conjugated become much smaller than they were 

 previous to the union. The filaments with the cells thus united 

 appear to the unassisted eye to be striated or banded. The 

 above account, as well as the description given in the c Annals 3 

 for September, apply to the species in its ordinary condition. 

 Two varieties of it however occur : in the first the filaments do 

 not differ in any material respect from the ordinary ones, but 

 all the cells of each filament unite to form spores, as in other 

 Zygnemata ; this they do also in the second variety, but in it 

 there are fewer spiral coils, usually six or seven, and these are 

 filled with much larger granules than those of either of the 

 previously mentioned conditions. The filaments of this va- 

 riety, which may possibly be a distinct species, from the small 

 number of the spires and large size of the granules, resemble 

 in all save diameter those of Zygnema nitidum. In all the 

 varieties, the spores are slightly oval, and are less than the 

 calibre of the cell which contains them, the cavity of which 

 they therefore do not fill. 



Zygnema interruptum. Filaments of considerable length, and 

 intermediate in diameter between those of Z. maximum and 

 Z. nitidum ; cells at the period of conjugation rather longer 

 than broad, previous to this however they are frequently 

 not half so long as broad; spiral coils numerous; spore 

 oval, equalling in breadth the diameter of the cell, but not 

 producing any inflation of it. 



This fine species comes next to Z. maximum in size. It is 

 estranged from Z. nitidum by the larger diameter of the fila- 

 ments and the greater number of its spiral coils, these being 

 not less than eight or ten; while from Z. belle, to which it 

 bears considerable resemblance, it may be distinguished by 

 a comparison of the filaments, which are considerably the 

 largest in Z. interruptum ; the number of spiral tubes is also 

 somewhat greater in this. As in Z. maximum, in its ordinary 

 condition, it is only every second or third pair of cells which 

 unite, the granules, as in it, become likewise largest in the cells 

 which have conjugated. 



