2. TabeUaria fenestrata, Kütz. Frustules definite ; septa 2 from
each margin, equal. Length of frustule -0008" to -0046"; inflations
of the valve nearly equal in width; striae as in the
last. v.v.
Kütz. Bacill. xvii. 22. Raben. Siissw. Diat. x. 1. Diatoma fenestratum,
Lyng. Tent. ixi. E? Ralfs, Ann. vol. 11. pl. ix. 4. ad specim. authen.
in herb. Jenn.
Fresh water : often with the last. Wareham, Dec. 1849 ; Studland, Dorsetshire,
Sept. 1853 ; Maam, Galway, and Botanic Garden, Belfast, July 1853 ;
Grassmere, Westmoreland, and Rackham, Sussex, Aug. 1853 ; River Lee, near
Cork, April 1855, W. Sm. Rackham, Oct. 1842, Mr. Jenner. Ormesby,
Norfolk, Aug. 1853, Mr. Brightwell. Haverfordwest, March 1854, Mr.
Okeden. Ulverstone, Lancashire, Aug. 1854, Miss E. Hodgson. Lough
Mourne and Lough Island Reavey Deposits. Dolgelly Earth. (Falaise,
M. De Brébisson. Pic de Sancy, Mont Dore, elev. 6000 feet, June 1854,
W. Sm.)
Very like the last iu the S. V. of its valve, especially in small specimens,
but always to be known from it by the definite structure of the frustule.
Plate XLIII. 317.
G e n u s 45. AM PH IT E TR A S , Fhr.
Frustules cubical, cohering into a zigzag attached filament; connecting
membrane cellulate, imperfectly annulate, indefinite;
valves quadrangular, cellulate ; cellules circular, radiate, or irregularly
concentric, inconspicuous at the angles of the valve.
The cubical outline of the frustules distinguishes the species
included in the present genus from all our other native forms. The
irregular development of the connecting membrane and its annulate
structure ally it to the several genera lately described; but the entire
absence of internal septa is a character which places Amphitetras
apart from TabeUaria, and, together with the zigzag of its filaments,
forbid its union with Rhabdonema or Tetraeyclus. The projection of
the connecting membrane beyond the suture of the valve is a circumstance
which meets us for the first time in Amphitetras; it will
also be found in Biddnlphia; and the enlarged appearance which is
thus given to the central portion of the mature frustule is a conspicuous
character in these genera.
1. Amphitetras antediluviana, Fhr. Frustules cubical; margins
on 8 . V. nearly straight, forming a square. Length of a side of
valve -0011" to -0042". v.v.
|3. Margin of valve deeply concave; frustule in consequence cruciform.
Distance between the adjacent angles of valve ’0025" to ‘0062". v.v.
Ralfs, Ann. vol. 12. pl. viii. 5. Kütz. Bacill. xix. 3. Prit. Anim. xiv. 21, 22.
Var. ft. Kütz. Bacill. xxix. 86.
Marine. Torbay, June 1846 ; Poole Bay, July 1849 and Sept. 1854, TV. Sm.
Haverfordwest, July 1854, Mr. Okeden. Ilfracombe, Mr. Ralfs. Torbay,
Mrs. Griffiths. Var. ft. Stomach of Crab, Professor Williamson. Ipswich,
Aug. 1852, Mr. Hodgson. Cumbrae, Feb. 1854, Mr. B. Hennedy. (Var. ft.
Salt Pans near Agde, South of France, May 1854, W. Sm.)
It is probable that the above Var. ft. has a claim to be esteemed a distinct
species. I have not found well-marked specimens of the two forms in any
instance intermixed, and the deeply excavated sides, and, in consequence,
cruciform outline of the frustule, are as notable in the smallest as in the largest
individuals of the Mediterranean gathering. 1 have distributed specimens
of the latter under the name of A. excavata; but, in deference to the opinion
of my esteemed correspondent Dr. Walker-Arnott, have determined to retain
it for the present as a variety of the more usual form.
Plate XLIV. 318. Var. ft. Plate XLIV. 318 a'".
G e n u s 46. B ID D U L PH IA , Gray.
Frustules compressed, adhering more or less perfectly into a continuous
or zigzag filament; valves convex, elliptical, usually
spinose and cellulate; cellules circular; angles of valves produced
into rounded or horn-like processes.
The frustules of Biddulphia are so various in outline, that it is
difficult to fix upon any constant generic characters descriptive of
their form; they all, however, agree in having compressed frustules,
with the angles of the valves produced, and in presenting a cellulate
structure, not only in the valves, but also in the connecting membrane.
The latter is frequently projected beyond the suture, and
appears as an encircling band of silex standing out from the general
surface of the valve. Frustules .of Eupodiscus, adhering after selfdivision,
often closely resemble Biddulphia ; they differ, however, in
the orbicular outline of their valves, and in the processes of the