I cannot discover tlie necessity for the genus Ulothrix. K ü t-
zing’s definitions of the genera Ulothrix and Sphoeroplea are as
follow : —
U lothrix — “ Trichoma simplex, membranaceum, tenerrimum,
flaccidum; cellulæ gelineæ, tenuissimæ, liyalinæ, ach-
romaticæ, abbreviatæ: amylideæ delicatissimæ, virides, ple-
rumque granullferæ, primo extensæ, dein paulatim in fascias
transversales contractæ, tandem in opseospermata quatuor vel
plura hologonimica transeúntes.”
SniÆROPLEA. — “ Trichoma parenchymaticum simplex,
cellulæ tenuissimæ membranaceæ, substantia chlorogonomica
demum in spermatia transeúnte repletæ, spermatia primo
vlridla delnceps miniate fusco : epispermio duplici, exterior!
fillforml, internum spiraliter investiente, cuneta in series longi-
tudlnaliter digesta.”
The endochrome in all the species of this genus in the
young condition is almost uniform ; subsequently, however, it
parcels itself into numerous zoospores in each cell. The
same remai’k applies to all the Algæ, which are multiplied by
means of zoospores.
The species described in this genus might with some propriety
he divided into two subgenera, in the first of which
should be placed Lynghya zonata, L . muralis, L . virescens, L .
Thonvpsoni, and L . copulata, in which the filaments are almost
always attached, are of a delicate and fragile nature, of a deep
green colour, and delight in pure water ; while in the second,
Lynghya fioccosa, L . punctalis, and L . vermicular is, should
be ranged, these being distinguished by characters the very
reverse of those ju s t enumerated, they being rarely attached,
tenacious, of a dull green colour, and inhabitants of impure
Avaters. In this division L.prolifica should also find a place.
1. L y n g b y a z o n a t a Hass.
Plate L IX . Pigs. 4, 5, 6 and 1, 2, 3.
Char. Filaments o f considerable diameter. Cells usually
rather longer than broad, hut sometimes shorter. Fndochrome
at fir s t quadrangular, not entirely filling the cavity
o f the cell, hut leaving a pellucid margin all around, subsequently
becoming globular and granular. Zoospores six
or eight in each cell.
Conf. zonata Web et Morh. Conf. lucens DIIIav. t. 47.
Conf. bicolor, F . B. t. 2288. Sphoeroplea crispa Berk.
Glean. Algæ, t. 3. fig. 1.
This species delights in pure and running Avater, it growing
luxuriantly in tha t of cascades and waterfalls. I t is everywhere
common throughout Great Britain. Considerable confusion
seems to have prevailed relative to this plant, several
observers having repeatedly described it under different names.
I have no doubt whatever of the correctness of the synonymes
quoted. The form of the cells in this species is somewhat peculiar.
They are not exactly cylindrical, b u t taper gradually
from each extremity towards the centre of the cell, the extremities,
or angles of the cells appearing in consequence
prominent.
Two varieties of it have presented themselves to me ; the
one at Snaresbrook, Fssex, in great quantity ; this agreeing
Avith the species proper in all, save the length of the
cells, which are generally two and a half or three times as
long as broad; the other in a stream at Wood Green, near
Cheshunt, in which the cells are cylindrical, completely filled
witli endochrome, and not one third so long as broad. This
may be distinct.
2. L y n g b y a m u r a l is Ag.
Plate L IX . Fig. 7.
Char. Filaments o f less diameter than those o f Lynghya
zonata, dark green, entangled. Cells very short, two or
three times broader than long.
Hab. On the ground in all damp situations early in the
spring.
This is a very distinct species, rendered interesting from
the peculiarity of its habitat. The diameter of the filaments