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Derivation. From gspts, a portion or particle.
This is a veiy natural genus, differing from Fragilaria in
the cuneate form of the frustules in the front view, and attenuated
outline in the end or lateral aspect, and from Stylaria
in tlie number of frnstules, which cohere, and which form
more or less considerable portions of circles.
1. Me r id io n cir cu la r e Ag.
P late X CV I. Figs. 1— 6.
Char. Frustules very variable in size, hroad margin, punctated.
Articulating surfaces clavate, strongly striated;
the ends o f the striæ appearing as puncta along the edges
in the fro n t vieio.
Meridian circulare Ag., Consp. Diatom, p. 40. ; Kiitz. Synop.
Diatom, in Linnæa, 1833, p. 558. f. 37. ; Harv.
Manual, p. 205. Meridian vernale, p. 207. t. 16. f. 2.
Bailey’s American Bacillaria, in Amer. Jour. Sci. Jan.
1842, pl. ii. f. 42. Fchinella circularis Crev., in W e rnerian
Society, vol. iv. p. 213. pl. viii. fig. 2., 1822; Scot.
Crypt. Fl. vol. i. t. 35. M. circulare Ralfs, in Annals,
vol. xii. p. 458. pl. xviii. f. 1. ; Jenner, in Flora of Tunbridge
Wells, p. 206.
Hah. Common throughout Creat Britain, in pools, &o.
The frustules of this very beautiful production exhibit all
the variety of sizes which characterise the different threads
of the Fragilarioe, and this resulting from the same cause, viz.
the lateral growth of the frustules. In the smaller and narrower
frustules the end view is broadly clavate ; in the larger
and deeper frustules it is but slightly so, indeed almost linear.
I have occasionally met with frustules which have been very
perceptibly curved; this form possibly arising from the
spiral disposition of the lamina in the more perfect specimens.
Colour yellowish brown, assuming a green tinge in drying.
2. M e r id io n constrictum Ralfs.
Plate X CV I. Figs. 7, 8, 9.
Char. Articulating surfaces constricted at the broader end,
striated; the striæ forming puncta in the fro n t vieio.
Meridion constrictum Ralfs, in Annals, vol. xiii. p. 458.
pl. xiii. fig. 2. ; Jenner, in Flora of Tunbridge Wells,
p. 206.
“ This is one of the additions to our Flora, for which I
am indebted to Mr. J enner, whose discoveries have added so
largely to the Sussex Cryptogamia, and who is as indefatigable
in his researches as he is accurate in his observations. Mr.
Jen n er finds it rather plentifully in the Cold Bath Spring,
Tunbridge Wells, growing on Fragilaria virescens. I have
received from him both dried and recent specimens. In the
latter I find the frustules solitary or binate, the circles being
entirely broken up before the specimens reached me ; but
Mr. J enner informs me, that when gathered, they are united
together so as nearly to form a circle. As, however, they
are not arranged on a plane as in Meridion circulare, but
stand nearly erect, somewhat like the staves of a tub which
is broader above than below, when they are dry and fall
down they necessarily separate, and gaps are produced in the
circular outline. In the dried specimens I find some of the
frustules arranged in a circle, which, however, exhibits the
gaps already noticed, whilst others seem to be fasciculated.
“ The front view cannot be distinguished from a frustule
of Meridion circulare, with which it agrees in size and form,
and also in having two conspicuous terminal puncta, and a
series along the lateral margins. As in Meridion circulare,
the lateral surfaces have a few distinct, strongly marked
transverse striæ ; but they differ from it most remarkably In
the constriction below the apex.” —■ Ralfs.
In the very deep frustules the constriction is almost lost.