gatherings from which Ehrenberg derived his specimens. I feel
assured that all the species of Biblarium are filamentous in a living
state, and that the greater number of them are casual varieties of
Tetraeyclus lacustris.
1. Tetraeyclus lacustris, Ralfs. Extremities of valve rounded or
subacute; inflations rounded; annuli 12 to 40, 6 in "OOl"; septa
alternate, equal in length. Width of filament '0008" to '0022".
Breadth of valve at the inflation -OOl". Costæ 7 to 12, 6 in
•001". v.v.
Ralfs, Ann. vol. 12. pi. iv. 2. 1843. Kiitz. Bacill. xxix. 70. Prit. Anim. xiv.
24,25. Raben. Siissw. Diat. pi. ix. Biblarium Stella, B. Gians, &uiB.
speciosum, Ehr. in Kiitz. Sp. Alg. p. 117, et Microgeologie, passim.
Fresh water. Dolgelly, Aug. 1843, Mr. Ralfs. Tonabrick Mountain, Co.
Galway, July 1853, W. Sm. River Spey, July 1854, Dr. Gregory. Dolgelly
Earth. (Lapland.)
Plate XXXIX. 308 : margin of a frustule, 308 x.
2. Tetraeyclus emarginatus, W. Sm. Valves constricted towards
the extremities, which are rounded and subapiculate ; inflations
deeply notched or emarginate ; otherwise like the last species.
Biblarium
passim
Ehr. in Kiitz. Sp. Alg. p. 118, et Microgeologie,
Fresh water. Mountain streams and cascades. Gap of Dunloe, Killarney,
July 1855, W. Sm. River Spey, Dr. Gregory. Killiecrankie, Dr. Greville.
In the Killarney gathering this form occurs abundantly, aud unmixed with
the last; but, in the River Spey, it is sparingly present along with undoubted
frustules of Tetraeyclus lacustris. It is possibly only a variety of the latter,
though its aspect is so different that the observer cannot fail to detect its presence,
and to regard it as distinct. I regret that it was noticed too late to be
figured in the present work.
G e n u s 42. DIATOMA, Dec.
Frustules oblong, adhering by their opposite, and alternate, or more
rarely by their adjacent angles into a zigzag chain; valves elliptical
or linear.
The position of the present genus, with its ordinary cell, in a subtribe
whose genera have annulate frustules, is somewhat anomalous;
but as our Synoptical arrangement is designed to aid in the identification
of species by a statement of the moat obvious characters, it
appeared necessary to place Diatoma, with its zigzag filament, near
others presenting a like notable peculiarity.
No difficulty can arise in the discrimination of the species of the
present genus. Fragilaria virescens is the only form which might
possibly be assigned to Diatoma; but this error will be avoided by
remembering that the zigzag, which is rare and accidental in F. virescens,
is a constant and distinctive feature in all species of the present
genus.
1. Diatoma vulgare, Bory. Valve elliptical, suddenly attenuate
towards the obtuse extremities, costate ; costæ pervious, somewhat
irregular, about 18 in -OOl". Length of frustule -0007" to -0021".
Breadth of V. -0003" to -0005". v.v.
ft. Valve linear, extremities gradually and slightly attenuate. Length of
frustule -0018" to -003". v.v.
Ralfe, Ann. vol. 11. pi. ii. 8. Kütz. Bacill. xvii. 15. Rahen. Sûssw-. Diat.
pi. ii. Hass. Alg. xciv. 1. B a c iUa ria v u lg a r is ,'Ehx.lvLi.s.Y. 2. Var./I.
Diatoma tenue, Ag. ad specim. authen. in herb. Grev.
Fresh water. Wareham, Dorsetshire, May 1849 ; Lewes, Sussex, April
and Sept. 1852 ; Glasheen, near Cork, April 1855, W. Sm. Ardrossan, April
1853, Dr. Landsborough. Lough Leven, Oct. 1854, Dr. Arnott. Var. ft.
Plumpton, Sussex, April 1852 ; River Lee, near Cork, April 1855, IF. Sm.
Pentland Hills, April 1821, Dr. Greville. (Canal du Midi, and Canal de
Crapone, South of France, ft. Fountain in Hotel des Colonies, Marseilles,
May 1854, W. Sm.)
Plate XL. 309. Var. ft. Plate XL. 309 ft.
2. D ia tom a g r a n d e , n. sp. Valve linear, constricted near the
rounded extremities, costate ; costæ pervious, 24 in -OOl". Length
offrustule -0013" to -0038". Breadth of valve -00025" to -0003". v.v.
Fresh water. River Lune, Lancashire, April 1848, Mr. G. Smith. River
Shannon and River Corrib, July 1853; Lough Derg, July 1855, W. Sm.
Lough Neagh, Dr. Dickie. Lough Leven, May 1854, Dr. Gregory. Allan
Water, Stirling, May 1855, Dr. Greville. (River Sorgues, Vaucluse, May
1854, W. Sm.)
I was at first disposed to assign this form to D. Ehrenbergii, Kutz. ; but as
Professor Kützing describes and figures the latter with a central inflation of
the valve, while the present is linear, and as authentic specimens of D. Fhren