species from those of Z . commune before conjugation: after
this lias occurred, the difference in the length of the cells and
the form of these is so obvious as not to leave any doubt of
its being distinct from that s^iecies. To this species ought, I
think, the Zygnema hrevissimum, described by me in vol. x.
p. 40. of the “ Annals of Nat. Hist.” to be referred. I am still
not sure, however, but that it is distinct, yet fear to regard it
as such. The cells in it are scarcely so long as broad; the
sporangia broadly oval, sometimes almost circular, their long
diameter being placed transversely in the cells, which are
frequently highly inflated.
17. Zygnema commune Hass.
Plate X X V I I I . Figs. 5, 6.
Char. Filaments about equal in diameter to those o f Z . cate-
naforme. CCds, usually three times jxs long as hroad. Sporangia
acutely oval, not occasioning any infation o f the
cells in which they are formed.
Zygnema commune Hassall, in Annals of Nat. Hist. vol. x.
p. 39.; Dillw. t. 3. upper figure, in part ?
Hah. Cheshunt: A. H. H. Framfield Common: Mr.
Jenner. Parkind Q u a rry : Major Martin.
Tliis is a very distinct and regular species.
18. Zygnema gkacile Hass.
Plate X X X . Figs. 5, 6.
Char. Filaments o f less diameter than those o f Z. commune.
Cells usually fo u r times as long as hroad, and inflated on
the side ivhich gives origin to the tubes o f communication.
Sporangia acutely oval, not rendering the cells at all ven-
tricose.
Hab. Wanstead Flats, Fssex ; Cheshunt: A. H. H.
Apparently a distinct species, knoAvn from Z. commune by
the smaller size of the filaments and lateral enlargements of
the cells.
19. Zygnema flavescens Hass.
Plate X X X . Figs. 9, 10.
Char. Filaments o f less diameter than those o f Z. catenm-
forme. Cells usually fo u r times as long as broad, and
slightly inflated fo r the accommodation o f the sporangia,
which are oval.
Hah. Hertford H e a th ; High Beech, F s s ex : A . H. H.
Several places in Sussex and K e n t: Mr. Jenner.
The only species with which this could be confounded are
Z. catenaforme and Z. parvum, between which it is intermediate.
I t seems to prefer, Hke several other species of the
genus, the boggy pools of heaths, &c., to roadside ponds and
ditches.
20. Zygnema paevum Hass.
Plate X X X . Figs. 7, 8.
Char. Filaments more slender than those o f the preceding
species. Cells rather more than fo u r times as long as
broad. Sporangia oval, generally producing a slight inflation
o f the cells in which they are formed.
Zygnema parvum Hassall, in Ann. Nat. Hist. vol. x. p. 41.
Hob. Che sh u n t: A. H. H. In a pond between Ramslye
Rocks and Broadwater F o re s t: Mr. Jenner.
This is one of the smallest species of the genus; it is not
uncommon.
** Extremities o f Cells inverted,
21. Zygnema Geevilleanum Hass.
Plate X X X I . Figs. 1, 2.
Char. Filaments o f rather less diameter than those o f Z.
curvatum. Cells usually six or seven times as long as
hroad, round the interior o f each o f which winds generally
one and sometimes two spiral threads. Sporangia broadly
L 3