crasterias Boryana Ehr., Infus. p. 157. pi. f. 5. a. c. x.
k, h, 1, f, g, but not b, c, d, e. Micrasterias tricyclia
Ehr., Infus. p. 158. pi. xi. f. 8. b, c, d, f, g, e, i, but
not a. Pediasti'um Boryanum Menegh., Synops. Desmid.
p. 210.; Bailey, American Bacil. fig. 20. Pediastrum
Boryanum Ralfs, in Annals, vol. xiv. p. 470. pi. xii.
fig. 7. in part 1.
Hah. Cheshunt, Herts: A. PI. H. Brambletye, near
Forest Row; Tunbridge Wells, &c. : Air. Jenner. Dolgelley
; Barmouth; and Penzance: Mr. Ralfs.
I t appears to me tha t more than one species has been confounded
together by different observers, and regarded as the
present plant. Ehrenherg has figured four species under
the name of Aiicrasterias Boryana, one of these being re-
ferrlble to the Micrasteidas tricyclia of Ehrenherg, pi. xi.
fig. 7. a, a plant which is British, and Mr. Ralfs, probably
three species, the one of these being doubtless identical
with Ehrenberg’s Micrasterias angulosa. The Pediastrum
Boryanum is the commonest species of the genus.
“ Sometimes plants are met with having more than three
circles: these are probably the Micrasterias elliptica Ehr.,
Infus. p. 158. tab. xi. fig. 9., which Meneghini refers to
the present species. I am not, however, satisfied that it is
not d istin c t: the external cells agree with the description
given above, but the inner ones are variable in number, and
not arranged in regular circles. Whether it possesses any
other distinctive character I have not yet clearly ascertained.
This form is fig. 21. of the American ‘Bacillaria.’ ” — Ralfs.
5. P ed ia strum tr ic y c l ium Hass.
Plate XCII. Fig. 1.
Char. Fronds usually constituted o f three circles, the inner
circle formed o f fo u r or fiv e cells placed round a central
cell, the second circle o f eight or ten cells, and the third
circle o f fifteen cells. Cells someuAiat quadriform, those o f
the centre as well as the marginal ones usually incised.
M. Boryana Ehrenherg, Infus. p. 157. pi. xi. fig. 5. i, b.
Micrasterias tricyclia, pi. xi. fig. 8. a, but not b, c, d,
e, f, g, h, i, k.
Hab. In a pond in a brick-field Notting H ill: A. H. H.
This appears to me to be a very distinct species. The
central cells are not always placed in exact apposition with
each other, frequently intervals or triangular interstices are
left between them. Ehrenherg has strangely confounded
the Pediastrum Boryanum with this species, and on the other
hand this species with P. Boryanum.
6. P ed iastrum angulosum Hass.
Plate L X X X V I . Fig. 14.
Char. Fronds constituted o f two concentric circles o f cells
surrounding a single central cell, the fir s t circle being
formed usually o f fiv e cells and the second o f ten. Marginal
cells alone incised.
Aiicrasterias angulosa Ehr., Infus. p. 158. pi. xi. fig. 6. Pediastrum
Boryanum Ralfs, loc. cit. p. 470. pi. xii. fig. 7.
in part 1.
Hah. England.
There can be scarcely a doubt of the distinctness of this
species. I t is figured hy Mr. Ralfs as the Micrasterias Boryana
Ehr., with which species it has no affinity. Mr. Ralfs’
figure accords closely with Ehrenberg’s of Pediastrum angulosum.
7. P ed ia strum constrictum Hass.
Plate L X X X V I . Figs. 15, 16.
Char. Frond large, composed o f two or three concentric circles
o f cells surrounding a single central cell, fiv e cells in the
inner circle, ten in second, and fifteen in the outer circle.
Marginal cells toothed, teeth constricted.
Pediastrum Bomjanum var. Ralfs, in Annals, pi. xii. fig. 8.
c c 4