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Polyedr ium tetra ed r icum. Nag. Einz. Alg.
Cells regularly tetrahedrioal; angles obtuse, muoronate.
S iz e . Cells -OIS-'OS mm. diam.
Rabh. Alg. iii. 62. Archer, Mior. Journ., 1866, p. 62.
In pools.
This might possibly be mistaken for the end view of some species of
Staurastrum, against which error it is essential that beginners should be
cautioned.
Plate X l l l . fig. 3. Cells magnified 400 diameters.
B. Angles radiato-elongated.
Poly edr ium lon g isp in um . {Perty.) Rahh. Alg. in ., 62.
Quadri-radiate, radii tliiHj elongated, scarcely thickened into
a body in the centre.
Size. Length of arms -03-05 mm.
Phycastrum longispinum, Perty Kl. Lebensf. t. xvi., f. 30.
In pools. N. Wales {A. W. Wills).
A peculiar species, which at first sight seems to have bnt little relationship
with the other species figured. I t is often found associated
with Desmids, and delights in similar localities.
Plate X ll l .f ig . 2. a, h, o, d, cells magnified 400 diameters.
C. Angles lohed,
P oly edr ium enorme. {Ralfsi) Rahh. Alg. in ., 63.
Cells irregnlarly tetrahedrical, with the angles produced,
hyaline, deeply bilobate ; sometimes repeatedly bilobed, with the
lobes mncronate.
S i z e . Cells *025-’04 mm. diam.
Staurastrum enorme, Balfs, t. 33, f. 11.
In pools.
^ “ Frond very irregular and variable in form. Sometimes the front
view differs but little from the end one. Usually, however, there is a
slight constriction at the junction of the segments, but I have never observed
any difference in the endochrome at that part. The spines, which
are almost confined to the angles, are irregular, some simple and some
branched. The end view has three or four broad and very irregular
lobes; these are spinous and more or less emarginate, and frequently
one lobe is much broader and more spinous than the others. The spines
on each lobe form two groups, separated by the notch ; they vary much
in size, and are either simple and subulate, or else forked; sometimes
the forked spines are again divided at the apex.”—Raljs.
A very variable plant, formerly included with the Desmidiese, but
separated on account of its different mode of propagation.
Plate X l l l . fig. 4. Cells magnified 400 diameters. Lateral and end
views.
Sub-Family 4 . S cen ed esm eíe .
Cells elliptic, oblong, or cylindrical; cell-membrane very thin ;
cell-contents at first bomogeneous, afterwards granular ; chlorophyllose
vesicle central or sublateral, and often a lateral colourless
spot; cells 2-4-16, either joined in a single series or forming
a cænobium. Propagation by division in the cells whence arise
gonidia, which unite themselves into a cænobium within the
mother-oell, and are a t length set free by the rupture of the
cell-membrane.
G e n u s 25. SCENEDESMUS. Wegem. (1829.)
Cells polymorphous, equal or unequal at the ends, often produced
into a spine-like horn. Frond or family composed of
from 2 to 8 oblong, fusiform, or elliptic cells, connecred into a
single or double continuous row ; propagating by means of the
repeated segmentation, in parallel planes, in one or two directions,
of each of the cell-contents into one or more brood families
(not motile), set free by the bursting of the parent-cell wall.—
Nageli.
A. Cells unarmed.
Scen ed e sm u s ob tu su s. Meyen. Ralh. Alg. in., 63.
Cells oblong or ovate, obtuse a t the poles, 4-6-8 loosely connected
in a simple series, or joined obliquely, 3-5 times as long
as broad.
S iz e . Cells •0055--007 mm. diam.
Ralfs Ann. Nat. Hist, xv., p. 404, t. 12, f. 8. Brit. Desm.
p 193, t. 31, f. 16. Archer in Pritch. Infus. p. 753, t. 1, f.
37-39. Hass. Alg. p. 394, t. 92, f. 15.
In boggy pools.
This species appears to be much less common than 8. quadricauda,
from all forms of which it may be readily distinguished, not only by the
difference in the form of the cells and absence of spines, bnt the remoteness
of one cell from its neighbour and their alternation.
Plate XIII. fig. 5. Cells in families of 4 and 8, magnified 400
diameters.
Sc en ed e sm u s a cu tu s . Meyen. Rabh. Alg.
Cells fusiform or ovate-fusiform, acute at each extremity,
2-4-6-8 united in a series, either single and straight, or double
and irregularly alternate ; 3-6 times as long as broad.
S iz e . Cells •0035--0055 mm. diam.
Ralfs Ann. Nat. Hist, xv., p. 404, t. 12, f. 6. Brit. Desm.
193, t. 31, f. 14. Hass. Alg. 893, t. 92, f. J4.
In pools and boggy places.
var. b. ob liq u u s. Rabh. Alg. ill., 63.
Cells elliptic, fusiform, arranged in two generally oblique
series, the outer cell of each not in contact with any of those in
the other series.
Scenedesmus ohliquus, Ralfs Desm. p. 192, t. 31, f. 15.
English Botany, t. 2933.
Scenedesmus triseriatus, Ralfs Ann. Nat. Hist, xv., p. 408, t.
12, f. 7.