or almost obsolete; cells of the disc perforated with smaller
openings.
Pediastrum tricyclum, Hassall Alg. t. 92, f. 1.
Pediastrum Napoleonis, Hassall Alg. t. 92, f. 10. (?)
Plate X V II. fig. 6. a, 5-oelled coenobiuin ; b, 16-oelled cænobium, flg.
4 ; /, marginal cell.
S ection 4. t e t b a c t i n i u m . B ra u n .
Cells of periphery emarginate or bilobate ; lobes emarginate,
bidentate, or bifid.
P e d ia s trum E h re n b e ig ii, Bv. Babh. Alg. in ., 72.
Cænobium orbicular or oblong, perfectly closed, composed of
8-16 colls, or quadrate, of 4 cells, which are wedge-shaped,
deeply lobed and arranged in the form of a cross ; cells of the
periphery cuneate, trmroato at the base, deeply bilobate; sinus
narrow, lobes obliquely truncate, more or less notched, interior
angles twice as long, all acute, or shortly appendioulate ; central
cells yellow green, polygonal, one side repand or deeply notched.
Pritch. Inius. t. 1, f. 52.
Pediastrum tetras, Ralfs Desm. t. 31, f. 1. Ralfs Ann. Nat.
Hist. xiv. (1844) t. 12, f. 4. Hassall Alg. t.^ 86, f. 17.
Pediastrum heptactis, Ralfs Ann. Nat. Hist. xiv. (1844) t.
12, f. 5. Ralfs Desm. t. 81, f. 2.
Pediastrum simplex, Hassall Alg. t. 8, f. 17.
Pediastrum biradiatum, Ralfs Desm. t. 31, f. 3, 4.
In pools and boggy places. Not uncommon.
Very variable in size. The 4-celled coenobia are often to be met
with, mixed with Desmids and other Algæ.
Plate X V I I . fig. 1. a, four-celled coenobia; h, 8-celled coenobia ; c,
8-celled cænobium of unusual form, after Ealfs.
var. a. t r u n c a tu m . Braun Unicell. Alg. p. 97.
Lobes truncate.
P ediastrum biradiatum, Ralfs Desm. t. 31, f. 4.
plate X V I I I . fig. 1. b, 8-oelled cænobia.
var. b. e x c is um . Braun Unicell. Alg. p. 97.
Lobes slightly notched, emarginate.
Plate X V I I I . fig. 1. d, 4-celled cænobium; e, 8-oelled cænobium;
i, k, 16-celled ooeuobia.
var. c. c u s p id a tum . Braun Unicell. Alg. p. 97.
Lobes deeply notched, evidently bidentate or biouspidate.
Pediastrum biradiatum, Ralfs Desm. t. 31, f. 3.
In stagnant water, throughout Europe generally.
Plate X V I I I . fig. 1. g,h, coenobia ; /, marginal cell.
P e d ia s tr um r o tu la . (Ehr.) Br. Unicell. Alg. p. 101.
Cænobinm orbicLilar or oblong, size and number of cells
variable, 4-8-16-82, pierced with openings, bright green, even ;
cells of the periphery truncate at the base, more or less dilated
upwards, deeply bifid, sinus acute, lobes straight, narrow, bidentate,
teeth erect or divergent, somewhat bent; cells of the
centre variable in form, usually polygonal, repand, or notched,
containing a single paler spot, sometimes not visible.
Eabh. Alg. iii. p. 79.
P ediastrum heptactis, Hassall Alg. t. 92, f. 9.
Pediastrum incisum, Hassall Alg. t. 92, f. 8.
In pools, &o., throughout Europe.
Plate X V I I I . fig. 2. b, marginal cell ; a, 4-celled cænobinm ; c,
6-celled cænobium ; d, 8-celled cænobinm ; e ,f, /i, 16-celled ooeuobium;
g, irregular cænobium.
Sub-Family 8 . S o r a s t e eæ .
Cells polygonal, often shortly horned, associated in a hollow,
sphærical or cubical cænobium ; cell-membrane thin ; cell-
contents green, homogeneous, then granular ; chlorophyllose
vesicle central or sublateral. Propagation by gonidia, in two
modes in the same species (simultaneous, or alter division),
united into a cænobium within the mother-oell, escaping by
rupture of the membrane.—Rahh. A lg . E u r . iii. 79.
Genus 30. COE LA ST R UM . Nag. (1849.)
Cænobium globose, hollow within, formed of a single stratum
of cells, reticulately pierced.—Rabh. A lg . E a r . iii. 79.
Erond, or family, hollow', globular, or subcubical, composed of polygonal
or sphærioal cells, united in one layer into a hollow clathrate net-
like family, the cells drawn out on the exterior into one or more lobes,
or simply sphærioal ; propagating by the segmentation of the oell-oon-
tents into a definite number of portions which become arranged into a
hollow young frond, resembling the parent, ultimately set free by the
bursting of the parent cell.—P7'itch. 755.
C æ la s trum s p hæ ric um . Ncig. B in. Alg. 97.
Cænobium globose or subglobose, composed of 4-8-16 or a
larger number of cells, perforated, areolæ 3-4-5-6 angled ; cells
rounded, by mutual pressure angular, outer angles somewhat
conical, obtusely rounded at the apex ; interstices 5-6 angled.
S i z e . Cænobium -Od-'OSb mm. diam. ; cells -021--023 mm.
Ccelastrum Naegelii, Rabh. Alg. iii. 79. Archer in Pritch.
Infus. p. 755, t. 1, f. 49-55.
In boggy places.
Plate X IX . fig. 2. n, b, families magnified 400 diameters; c, cell
magnified 800 ; d, cell of C. cubicum, with two obtuse processes ; e, cell
cf Coelastrum, perhaps C. caiiibricmn, with one obtuse process.
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