Section ii.
Frond stipitate.
A. Frustules wedge-shaped.
75. GOMPHONFMA Ag.
Char. Frustules cuneate, solitary or geminate, supported on
a simple or branched and attached filiform stipes.
Derivation. From gogfos, a wedge, and vyga, a thread.
The extremities of the frnstules in the front view are
punctated and truncated, hut in the lateral aspect rounded
or pointed ; tlie frustules are for the most part striated latc-
i-ally, tlie striæ being intcrrnpted by a longitudinal pellucid
line, in the centre of which is a depression often assuming
the appearance of a foramen. The genus hears a close relation
to the genera Styllaria and Lichmophora, the former
genus differing only from Gomphonema in the frustules being
invariably sessile, and the latter in having several frustules
associated together at the end of each branch of the stipes,
and forming a fan-likc expansion.
The species of the genus Gomphonema are usually found
in freshwater.
a. Frustules in lateral view constricted beloio the apex, so as
to appear urn-shaped.
1. G omphonema geminatum Ag.
Plate X C V I II . Fig. 1.
Char. Stipes much branched, tufted. Frustules large, cuneate,
often geminate, puncta at the end obsolete. Lateral
surfaces urn-shaped, striated. Striæ radiating.
Ag. Syst. p. 12.; Conspect. Diatom, p. 35.; Grev. Crypt.
Fl. t. 244. f. 2.; Kiitz. Synop. Diatom, in Linnæa, 1833,
p. 569. ; Harv. British Algæ, p. 207. Gomph. ampul-
laceum Grev., in Hook. Br. Fl. p. 410. G. geminatum
Ralfs, in Annals, vol. xii. p, 460. pl. xviii. fig. 3.
llah. On rocks in subalpine streams, Scotland : Dr. Greville.
North of Ireland : Air. D. Aloore. Near Bandon,
CO. Cork : Prof. G. J. Allman. On dripping rocks,
near a waterfall at Carnlough, co. Antrim ; Air. W.
Thompson. Eapid streams at base of Cader Idris;
and in the river above Dolgelly, North Wales: Mr.
. Ralfs.
“ This plant forms large cushion-like tufts on the rocks in
rapid streams. It is not in the least mucous, but is of a
spongy texture, being composed of densely interwoven
filaments. In a young state its colour is brownish, from the
frustules covering the surface; but as these fall off it becomes
whitish, and indeed not unlike a tuft of wool. Filaments
repeatedly dichotomous ; frustules much larger than in any of
the following species, simple or binate, linear cuneate, without
puncta at the upper end ; portions of the lateral surfaces
are frequently visible along the sides. Lateral surfaces urnshaped,
broader than the front, with numerous transverse
dotted striæ. There is a central longitudinal pellucid line,
slightly dilated at each end with a larger dilatation in the
centre ; the.latter at first sight may be taken for a perforation,
which it undoubtedly is not : from the central punctum the
striæ are somewhat radiant : the pellucid line does not quite
extend to the upper end.” — Ralfs.
2. G omphonema truncatum Ehr.
Plate X C VIII. Fig. 2.
Char. Frustules in front view cuneate, with two evident puncta
at the upper end. Lateral surfaces urn-shaped, striated.
G. truncatum and G. paradoxum Fhr., Abhandl. der
Alvademie d. Wissensch. zu Berlin, 1831, p. 88. 1833,
p. 319. G. pohliæforme Kiitzing, in Linnæa, 1833,
p. 569, 570. t. xvi. fig. 50. G. truncatum Ehr., Die
Infus. p. 216. pl. xviii. fig. 1. G. suhramosum Kiitz.,
Synops. Diatom, p. 570. fig. 44. G. pohliæforme Ealfs,
in Annals, vol. xii. p. 461. pl. xviii. f. 4. G. capitatum
E E 3