Mr. Hassall's Notices of British Freshwater Conferva* 433 



Zygnema rivulare. A variety of this species, described in the 

 1 Annals* for September 1842, is sometimes met with during 

 the autumn in water-courses, which differs from the ordinary 

 condition of the species in having cells varying in length from 

 twice to four times their diameter, and in being of a deep green 

 colour. The species in its ordinary state is generally found 

 attached to stones, and in streams near the margin where the 

 current is slow. In specimens procured from such places the 

 filaments are of a yellowish green colour, and the cells much 

 longer. There is no question of the specific identity of the 

 variety with the species proper. 



Zygnema cestivum. Filaments of less diameter than those of 

 Z. quininum ; cells usually about four times as long as broad, 

 but sometimes much longer and occasionally shorter. A 

 single spiral tube occupies the cells, passing from side to side 

 in right lines. 



This species is by no means uncommon, and was for a long 

 time confounded by me with the Z. quininum of Ag., from 

 which it differs in its smaller filaments, longer cells, and pe- 

 culiar zigzag disposition of the single spiral tube. 

 Cheshunt. 



Genus Mougeotia. 



Mougeotia brevior. Filaments about equal in diameter to 

 those of Mougeotia genuflexa ; cells usually twice as long as 

 broad, but sometimes nearly four times as long. Conju- 

 gation angular, without the intervention of tubes. 



I do not think that there can be any question of this being 

 specifically distinct from M. genuflexa, to which species its 

 filaments however bear considerable resemblance, owing to 

 the endochrome being of the same yellowish green colour. 



Vicinity of Cheshunt. 



Mougeotia dubia. Filaments about equal to those of M. genu- 

 flexa in diameter ; cells usually either four or eight times as 

 long as broad, but mostly only four times. Conjugation 

 angular and without the intervention of transverse tubes. 



This species may possibly be merely a variety of M. genu- 

 flexa, a doubt which I have indicated in the provisional name. 

 Vicinity of Cheshunt. 



Mougeotia flava. Filaments about equal to those of M, major ; 

 cells varying in length from rather better than twice to nearly 

 five times their diameter, but being generally three or 

 three and a half times as long as broad. Conjugation an- 

 gular, without the intervention of tubes. 



