Mr. H assail' s Notices of British Freshivater Conferva. 41 



filaments ; and from Z. subventricosum, on the other, by the 

 less considerable diameter of its filaments, as well as by other 

 characters. 



New River Reservoir, Cheshunt. 



Zygnema parvum. Filaments very slender ; cells rather more 

 than four times as long as broad, each containing about two 

 turns of a single spiral tube ; spores generally producing a 

 slight inflation of the cells. 

 The filaments of this species are nearly as slender as those 



of Z. tenuissimum, from which it may be distinguished by its 



much shorter joints. 

 Vicinity of Cheshunt. 



Zygnema tenuissimum. Filaments extremely slender; cells 

 about nine times as long as broad, each containing five or 

 six revolutions of a single spiral tube ; spores producing a 

 slight inflation of the cells. 



This species is to be distinguished from all others of the 

 genus which I have met with by the minuteness of its fila- 

 ments. 



Vicinity of Cheshunt. 



** Seeds produced without conjugation. 



Zygnema quadratum. Filaments at first cylindrical; cells 

 about nine times as long as broad, each containing from 

 six to seven revolutions of a single spiral tube ; spores oval, 

 large, and much elongated, contained within quadrangular 

 enlargements of the cells ; tube of communication arising 

 from the point of junction of two cells. 



I find this remarkable species very abundantly in ponds on 

 Cheshunt Common. 



Zygnema intermedium. Filaments nearly equal in diameter 

 to those of Zygnema quadratum ; cells about five times as 

 long as broad, round the interior of which a single spiral 

 tube performs about four revolutions ; spores oval, smaller 

 than those of the preceding species, and not contained in 

 quadrangular enlargements of the cells, but still producing 

 a slight inflation of them : tube of communication placed at 

 the junction of two cells in the same filament. 

 I have no doubt of this being specifically distinct from the 



preceding. It occurred abundantly to me at High Beech, 



Epping Forest, and I have since met with it in other localities. 



Zygnema angulatum. Filaments at first straight, but at the pe- 

 riod of reproduction becoming angulated, the angles being 

 situated at the passage of communication set up by means 



