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vexity in the end view, and the different character of the
marginal striæ. Owing to the frustules being convex, not
merely in thickness, but having rounded extremities, the
striæ are evident on a portion of the front surface.
The species grows most luxuriantly in gently running
water, frequently investing Cladophora glomerata, and causing
it to appear of a deep brown or chocolate colour. I t is attached
to this plant by means of a stipes, fii'st detected by
]\Ir. Jenner, the existence of which from its locality in flowing
water might have been predicted.
In drying it changes to a greenish hue.
2. D iatoma elongatum Ag.
P late X C IV . Figs. 3, 4, 5, 6.
Char. Frustules many times as hroad as long, at fir s t with
straight margins, subsequently, when fu lly developed, the
sides are dilated on the fro n t surface. End view linear,
loith slightly incrassated ends.— ß cuneatum. Frustules
icedge-shaped.
Diatoma tenue Ag., Consp. Diatom, p. 52. D. tenue 8
normale Kütz., in Linnsea, 1838, p. 580. t. 17. f. 63. D.
elongatum Berk., Glean, t. 6.; Hook. Br. Fl. 406.; Harv.
Manual, p. 202. D. sulphurascens Ag., Consp. Diatom,
p. 53. Conf. flocculosa Dillw., Br. Conf. t. 28. f. c. ?
Bacillaria pectinalis Ehr., Infus. p. 198. pl. xv. fig. 4. in
part only. D. elongatum Ag., Syst. p. 4. ; Kütz. in L in nsea,
p. 582. t. 17. f. 65. Bacillaria elongata Ehr., In fus.
p. 218. f. 169. D. tenue and D. elongatum Ralfs,
in Annals, vol. xi. p. 451, 452. pl. ix. fig. 1. ; D. tenue
Jenner, loc. cit. p. 202. Bacillaria cuneata Ehr., Infus.
t. X V . f i g . 6 . Diatoma tenue g cuneatum Kütz., in L in nsea,
1833, p. 580. t. 1?. fig. 62.
llah. Pools and streams. Near Tunbridge Wells : Mr.
Jenner. Shrewsbury: ilfr. AezV/AZow. Cheshunt: A. if . if .
Bangor, and Dolgelly, North Wales; Penzance: Mr.
Ralfs. Aberdeen : Dr. Dichie.
Rev. D. Landshorough.
Stevenston, Ayrshire:
This is a very variable species. In the young state the
frustules are plain, but in their fully developed condition
they are dilated laterally, or as most writers would say, at
each extremity. These two states have been separately described
as distinct species, but I have no hesitation in uniting
them. I have preserved the specific appellation of elongatum
in preference to th a t of tenue, because the latter term was
applied by Ehrenherg to the condition of the species with
dilated frustules, in fact to the species in its fully developed
or perfect state.
The younger frustules in the end view are slightly dilated
in the centre with incrassated ends; in this state they bear a
slight resemblance to the older ones of Diatoma vulgare, hut
are much smaller. The fully developed frustules in the end
view are linear and very slightly incrassated.
Remai-kable as the variety with cuneate frustules is, it is
I suspect but an anomalous condition of the species.
L ig h t brown or yellow when recent, assuming a faint
green tinge in drying.
3. D iatoma virescens Hass.
Plate XCV. Figs. 7, 8.
Char. Frustules usually two or three times broader than long,
frequently cohering together in the manner o f a F ragilaria.
In end view oval, with slightly constricted extremities.
Striæ inconspicuous.
Lragilaria pectinalis Yhx., Die Infus. p. 206. t. 16. f. 1.
excel, a ; Pritch. Infus. p. 222. fig. 176. Lragilaria
virescens Ralfs, in 1. c. p. 110. pl. 11. fig. 6. ; Jenner,
1. c. p. 202.
Hab. Cold bath spring, Broadwater F orest ; Lower
Green ; Rotherfield and Piltdown Common : Mr. Jenner.
Madron and Chyanhal Moor, near Penzance :