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1. P e d ia s t r um t é t r a s Ealfs.
Plate L X X X V I . Fig. 17.
Char. Frontls small, cruciform. Cells four, deeply hipartite.
Divisions, truncate, emarginate.
Aiicrasterias tetras Ehr., Infus. p. 155. t. xi. f. 1. Ilete-
rocarptlla tetracarpa Bory de St. Vincent, Diet.
Classique dTIist. Nat. 1825. Heterocarpella polymorpha
Kützing, in jiart, Linnæa, 1833, t. xix. fig. 82.
Stauridium bicuspidatum, Stauridium crux melitensis
Corda, Almanac de Carlsbad, 1835, pi. iii. figs. 33, 34.
Pediastrum tetras Kalfs, in Annals, vol. xiv. p. 469.
pi. xii. fig. 4.
llah. Barmouth and Penzance : ilfr. Ralfs. Beckley
F urnace, near Battle, Sussex : Air. Jenner.
A very rare and elegant species, and one of the least variable
of the genus.
2. P ediastrum simplex Hass.
Plate L X X X V I . Fig. 18.
Char. Frond constituted o f seven cells disposed in a circle, containing
in the centre one or tioo other cells which are emarginate.
Divisions o f the marginal cells slightly dentate..
Pediastrum heptactis Ilalfs, in loc. cit.
Hab. Barmouth : ilfr. Ralfs. Beckley Furnace : Mr.
Jenner.
Distorted fronds of this species frequently occur, in which
the central cell is altered in form and displaced in situation.
See PI. LXXXVI. fig. 18. a. Meneghini describes a single
hyaline vesicle in each cell.
Under the name of Micrasterias heptactis. Ehrenberg seems
to me to have figured two species, fig. 4. a. t. xi., being different
from b, c, d, which certainly represent the present
plant.
3. P ediastrum elegans ffes«.
P late L X X X V I . Fig. 19.
Char. Frond circular, star-like, composed o f six marginal
crescentic cells, and two central cells o f an angular form.
Pediastrum Napoleonis Kalfs, in Annals, vol. xiv. p. 470.
pi. xii. fig. 6.
Hah. Dolgelly : ilfr. Ralfs.
The above species, described and figured by Mr. Ralfs
under the name of Pediastrum Napoleonis, and as the Aiicrasterias
Napoleonis of Ehrenherg bears no resemblance whatever
to the figures given of that species, nor indeed to any
of Ehrenberg’s figures, save a distant one to fig. 5 e. of pi. xi.,
which is regarded by the author as a state of Micrasterias
Boryanum, which it certainly cannot be, as the frond in the
figure alluded to is made of ten marginal crescentic cells, and
five internal angular cells.
4. P ediastrum B oryanum Menegh.
Plate L X X X V I . Fig. 13.
Char. Frond composed usually o f two circles o f cells, enclosing
a central cell, but sometimes there are three and
even fo u r concentric circles, inner circle formed o f fiv e
cells, and second circle o f ten. Marginal cells deeply bifid.
Helierella Bory ana Turpin, Mém. du Mus. vol. xvi. p. 319.
pi. xiii. fig. 22. 1828. Pediastrum simplex, P. duplex,
P. biscidiatum Meyen, Nov. Act. Nat. Cur. xiv. 1829, p.
772; 773. t. 3. figs. 7. 13, 14. 16, 17, 18. ; Isis, 1830,
p. 163. Opharium speciosum, O.formosissimum, et O. ver-
ticillatum Losano, Mem. de Zarino, xxxiii. 1829 ; Isis,
1832, p. 768. t. xiv. figs. 17, 18. 21. Micrasterias simplex,
M. Boryi, M. duplex, et M. Selanæa Kützing, L in næa,
1833, p. 601. 3. t. xix. fig. 92 b. Euastrum
pentangulare et Pediastrum quadrangum Corda, Almanac
de Carlsbad, 1835, p. 206. 7. t. iii. figs. 32. 35. Mic
e 3