§1 '
Ith
‘Ml
Sussex, September 1853. Landport, Sussex, December 1853, &c., PF. Sm.
Aberdeenshire, November 1861, Dr. Dickie. (Vaucluse, Le Puy, Puy de
Dôme, Source of the Loiret near Orleans, and Champs Elysees, Paris, 1854,
The only species with which this universally distributed form can be confounded
is the last ; but from this a careful examination will enable the
observer to separate it. M. varians has the extremities of its frustules
closely applied and partially truncate ; those of M. subflexilis are often more
or less separated hy a mucous cushion, and distinctly convex. The latter
species has never occurred to me except in water under marine influences.
M. varians is found in every clear spring and river, from the lowest to the
most elevated situations. M. subflexilis, when found in abundance, appears
as a dark green iridescent mass. M. varians always presents a rich golden-
yellow or chestnut hue to the eye. The gemmate arrangement of the frustules
is conspicuous in M. subflexilis, and indistinct in M. varians. The two
species have been often confounded, but I think the differences they present
are quite sufficient to warrant their separation.
Plate LI. 332.
5. Melosira nivalis, n. sp. Frustules subcylindrical; valves sub-
hemispherical, distinctly cellulate; cellules circular; extremities
of valves more or less truncate. Breadth of filament -0002" to
•0 0 0 /". v.v.
Fresh water ; alpiiie pools. Snow mud, Ben M' Dhui, elev. 2800 feet. Dr.
Dickie. Pass of K.illiecrankie, August 1854, Dr. Greville. Mull Deposit,
Dr. Gregory. (Pic de Sancy, elev. 6000 feet, June 1854, W. Sm.)
The present species hardly differs from the next except in the greater
distinctness of the cellules, a character probably insufficient to justify their
separation.
Plate LIII. 336.
6 . Melosira distans, Kiitz. Frustules subglobular; valves sub-
hemispherical, obscurely cellulate. Breadth of filament '0002" to
•0009". v.v.
Kiitz. Bacill. Ü. 12. GalUonella distans, Ehr. Microg. tab. xv. F. ad specimina
authentica.
Freshwater. Elgin, August 1854, Dr. Gregory. Braemar, August 1854,
Dr. Balfour. (Puy du Capuchin, Mont Dore, elev. 4567 feet, June 1854,
W. Sm)
Plate LXI. 385.
7. Melosira W e s tii, n. sp. Frustules subglobular; valves conical,
with truncated apices, and a sutural and median siliceous ring.
Breadth of filament -0008" to -0016". v.s.
Marine. Stomach of Pecten, Coast of Sussex, W. Sm. ; detected by Mr.
West, March 1852.
Plate LII. 333.
G e n u s 50. O RTH OS IR A, Thwaites.
Filament cylindrical, of numerous frustules, continuous, attached or
free ; frustules and valves cylindrical ; junction-surfaces plane, line
of junction usually spinous or denticulate.
1. Orthosira arenaria, W .Sm . Filament curved ; cell-cavity sub-
spherical ; valves with a subsuturai line of puncta ; line of junction
with numerous minute denticulations or spines ; junction-surfaces
marked with radiating striae. Breadth of filament '0026" to
•0051". v.v.
Melosira arenaria, Moore in Balfs, Ann. vol. 12. pl. ix. 4. Kiitz. Bacill.
xxi. 27. Baben. Süssw. Diat. ii. 5. Melosira arenosa, Hass. Alg. xciii.
2 & 3. GalUonella varians, Ehr. Inf. xxi. 2. G. varians, undulata, et
, Ehr. Microgeologie.
Fresh water. Wareham, Dorset, June 1848, W. Sm. Westerham, Kent,
Dec. 1843, Mr. Jenner. Near Belfast, Dr. Dickie. Surrey, Mr. Capron.
Berwickshire, Dr. Arnott. Queen’s Park, Edinburgh, April 1854, Dr. Greville.
Lough Mourne and Peterhead Deposits, &c. (Falaise, M. De Brebisson.
Source of the Loiret, near Orleans, June 1854, W. Sm.)
In this aud the two succeeding species, the cell-cavity of each frustule is
more or less spherical, while the siliceous epiderm is cylindrical; hence the
margins of the filaments are direct and continuous, and no depressions are
conspicuous at the points where the frustules are united.
The filaments of 0. arenaria, when dry, are of a purple colour, and exhibit
a rich metallic lustre. They run no risk of being confounded with those of
any other form; and it is difficult to account for the confusion into which
Ehrenberg has fallen with regard to the present species, to which he seems to
apply indiscriminately the names of GalUonella varians, G. biseriata and
G. undulata.
Plate LII. 334.
2 . Orthosira marina, W. Sm. Filaments d irec t; cell-cavity sub