notched nor lobed, but mostly either denticulated or dotted,
almost touching each other.
Derivation. From Koagapiov, a small ornament.
The form of the frond in this genus is much more simple
than that of most of the other genera of Desmideæ, being
neither notched nor lobed. The genus to which it is most
closely allied is Xanthidium, from which it chiefly differs in the
minuteness of the spines or teeth, which are placed on the
outer surface of the frond in most species, as well as in the
absence of the lateral apertures noticed in Xanthidium f u r catum
and X . aculeatum. Through Closterium cylindricum,
it exhibits some relation to the genus Closterium, in which
the form of the frond is also very simple ; but the two genera
are abundantly distinct. In Cosmarium the fronds are never
elongated nor curved as in Closterium, and they are always
constricted in the centre ; neither are they notched as in
Tetmemorus and Euastrum, nor lobed as in the la tte r genus,
nor compressed as in Alicrasterias.
The denticulations observed on the surface of the fronds
of most species of the genus vary according to the age of the
specimens, being most strongly marked on the more fully developed
examples.
a. Fronds denticulated.
1. Cosmarium margaritieerum Menegh.
Plate L X X X V I . Fiff. 1.
Char. Fronds denticidated. Segments broader than long,
somewhat hemispherical or reniform, cpmpressed. End
view elliptic,
fl Fronds dotted, but not denticulated.
Menegh. Synop. Desmid. in Linnæa, 1840, p. 219. Cosmarium
dentiferum Corda, Observ. Microscop, sur les
Animale, de Carlsbad, p. 30. pl. vi. f. 41. Euastrum
margaritiferum Ehr., Infus. p. 163. tah. 12. f. 7.; Pritch.
JÌL
Infus. p. 196. f. 126.; Bailey, Amer. Bacil. in Am.
Journ. of Sciences and Arts, vol. xii. No. 2, p. 295. fig. 8.
UrsinellamargaritiferaYvx-p., Diet, des Sc. Nat. (1820).
Heterocarpella Ursinella Kiitz., Syn. Diatom, p. 598.
Cgmbella reniformis Ag., Consp. Diatom, p. 10. ; Grev.
in Hook. Br. Flor. vol. ii. p. 415.; Harv. Brit. Alg.
p. 215. Cosmarium margaritiferum Kalfs, in Annals of
Nat. Hist. vol. xiv. p. 393. pi. xi. fig. 4. ; Jenner, in
loc. cit. p. 194.
Hab. In bogs and pools, &c. common; Weston bogs,
near Southampton, and numerous habitats in Sussex
and K e n t: ilfr. Jenner. Farnham, S u rrey : ilfr. Reeves.
Cheshunt, H e r ts : A . H. H. Near B risto l: ilfr. Thwaites.
Barmouth : Rev. T. Salwey. Dolgelly, Carnarvon, and
Penzance: ilfr. Ralfs.
This species varies considerably in size, form, and in the
number and degree of developement of the spines, which
cover the frond. Each segment may be compared in form
to a kidney. I t is the most abundant species of the genus.
Ehrenherg figures the denticles as placed in regular series
or rows, which in some specimens I have seen to be the
case.
2. Cosmarium B otrytis Menegh.
Plate L X X X V I . Fig. 2.
Char. Frond denticulated, compressed. Segments truncatotriangular.
E nd view elliptic.
C. Botrytis Meneg., Synop. Desmid. p. 220. Euastrum Botrytis
Ehr., Infus. p. 163. tab. xii. fig. 8. C. Botrytis
Ealfs, in Annals of Nat. Hist., vol. xiv. pi. xi. fig. 5.
Heterocarpella Botrytis Bory, in Diet. Classique, 1825.
Euastrum dngidosum Ehr., Infus. tah. xii. fig. 8. Cos-
marium deltoides, in part, Corda, Almanac, de Carlsbad,
1835, p. 205.
Hab. Near Bristol: 3Ir. Thwaites. Sussex: Mr, Jenner.