. "l
li ii
bergii, Kütz., kindly sent me by M. De Brébisson, rmdoubtedly belong to the
next species, I bave felt myself obliged to sever this beautiful form from its
association with a naturalist who might otlierwise worthily claim the honour
of giving his name to one of the finest of the Diatomaceæ.
Plate XL. 310.
3. Diatoma elongatum, Ag. Valve linear, extremities slightly inflated,
rounded, costate ; costæ pervious, 18 in •001". Length of
frustule '0016" to -0042". Breadth of valve •00015" to '0002". v.v.
¡3. Frustules inflated towards the extremities. Length-0011" to '0025". v.v.
y. Frustules minute ; valve elliptical. Length -0004" to -0009". v.v.
2. Frustules distorted, irregular. Length-0004" t o -0011". v.v.
Ag. Syst. p. 4. Kiitz. Bacill. xvii. 18. Raben. Süssw. Diat. pi. ii. Dia-
toma tenue, Ralfs, Aim. vol. 11. pi. ix. 1. ad specim. authen. iu herb.
Grev. Var. ¡3. Diatoma Ehrenbergii, Kütz. Bacill. xvii. 17. ad specim.
quæ dedit am. De Brébisson. BaciUaria elongata, Ehr. Inf. xv. 5.
Prit. Anim. iii. 169. Diatoma elongatum, Ralfs, Ann. vol. 11. pl. ix. 2.
Hass. Alg. xciv. 3. Var. y. Diatoma tenue, Kûtz. Bacill. xvii. 9, 10.
BaciUaria flocculosa, Ehr. Inf. xv. 9. BaciUaria cuneata, Ehr. Inf.
XV. 6 .
Fresh or brackish water. Var. a. and;3. Poole Bay, March 1850 ; Lewes
March 1852 ; Denton, Sussex, Nov. 1853; Cork Harbour, April 1855,
W. Sm. Belfast, Dr. Dickie. Hornby, Lancashire, May 1853, Mr. G. Smith.
Hull, Aug. 1853, Dr. Arnott. Tunliridge Wells and Rackham Common,
Sussex, Mr. Jenner. Var. y. Tarring Neville, Sussex, Nov. 1853, W. Sm.
Ayrshire, March 1854, Dr. Bandshorough. Var. b. Hornby, Lancashire,
May 1854, Mr. Johnson. Sheriffmuir, Dr. Arnott, October 1855. (Var. b.
Well near Marseilles, May 1854, W. Sm.)
This most changeable species has received from observers almost as many
names as it presents diversities in size, and yet I feel persuaded, from a wide
comparison of specimens, that all the forms I have indicated must be regarded
as varieties of the same, dependent upon the stages of its growth, or the
circumstances which attend its development.
, Var. ¡3, which has been the most confidently separated from the type, is
perhaps the least constant of any in the character which has been relied upon
as a distinction ; frustules with the extremities inflated on a front view, or
rather those in which the connecting membrane has slightly collapsed towards
the centre of the frustule, being almost invariably found intermixed with
others of a perfectly oblong outline, and the two not unfrequently occur
together in the same filament. Even the singular variety figured in Plate
XI.I. 311 y . f , and which Ehrenberg has placed apart as BaciUaria cuneata,
will be seen to be accidental, and is found in association with frustules
undoubtedly belonging to the normal form.
The bizarre forms, produced by the capricious mode in whicii the partial
separation of the frustules in the chains is effected, have also occasioned confusion
; but a little study of specimens from various localities, and collected
at different seasons, will satisfy the student of the impropriety of relying upon
these accidental peculiarities as the bases of specific distinction.
The present may be distinguished from the last species, not only by its
smaller size, but by the inflation of the extremities of the valves. In
D. grande the apparent enlargement of the extremities is produced by a constriction
; in D. elongatum the extremities in the mature frustules are absolutely
wider than any other portion of the valve.
Plate XL. 311. and PI. XLI. 311. Var. ¡3. PI. XLI. 311 ¡3. Var. y.
PI. XLI. 311 y. Var. g. Supp. Plate LX. 311 g.
4. Diatoma hyalinum, Kütz. Filaments of numerous frustules ;
valve linear-elliptical, extremities somewhat acute; striæ obscure.
Length of frustule -0008" to -0052". Breadth of V. about 'OOOS".
Kütz. Bacill. xvii. 20, et Viatoma vitreum, Kütz. Bacill. v. 7, xvii. 19, xxiv. 1.
ad specim. authen. quæ dedit amie. De Brébisson. Striatella toeniæformis,
var. a, Ralfs, Trans. Bot. Society of Edinburgh, vol. ii. p. 22?
Marine. Jersey, Aug. 1852 ; Larne, July 1853 ; Newhaven, Sussex, Aug.
1853, W. Sm. Saltcoats, Oct. 1853, Dr. Arnott.
Plate XLI. 312.
5. Diatoma minimum, Ralfs. Filaments of two or three frustules ;
valve elliptical ; extremities rounded ; striæ obscure. Length of
fru stu le ’0002" t o -0004". Breadth of V. a b o u t-OOOlò". v.v.
Ralfs ill Trans. Bot. Society of Edinburgh, vol. ii. p. 20 ?
Marine : parasitic upon frustules of Surirella Gemma. Hove, Sussex, Sept.
1853, W.Sm.
I cannot refer this form with certainty to Mr. Ralfs’ species, not having
seen specimens of the latter ; the present, however, agrees with Mr. Ralfs’
description, “ Frustules very minute, about twice as long as broad.”
Plate XLI. 313.