RoPER^ on Biddulphia. 
11 
leave nothing to add as to its general structure. Agardh 
founded his genus Odontella on this species^ apparently from 
the presence of the spines on the summit of the central infla- 
tion, as the only description he gives of the genus, is 
Frustilla dentibus cohserentia filum formantia/^"^ Kiitzing, 
both in his ^ Bacillarien/ and also in his later work, the 
Species Algarum/ retains a large number of species under 
that generic name. The valves in this species vary consider- 
able in outline, and though usually elliptical-lanceolate, as 
stated by Professor Smith, they occasionally occur of a nearly 
perfect oval. (See Plate I, fig. 3.) They are, however, 
readily distinguishable from all others of the genus from the 
presence of the central elevation, with three or more spines 
on its summit, which is merely a circular projection of a 
portion of the valve, and does not extend across it, as in 
B, reg'ina, nor is it separated by constrictions or costse; as is 
clearly shown in fig. 319 « of the ' Synopsis.^ 
5. Biddulphia rhombus, Ehr., sp. Synopsis,^ p. 49.) 
Marine or brackish water. In addition to the localities 
noticed by Professor Smith, in the ^ Synopsis,^ it has been 
found in a living state near Tenby by the Rev. J. Guillemard, 
in various localities in America by Professor Bailey, in the 
Baltic and North Sea by Ehrenberg, and at Gorleston by 
Col. Baddeley. (Plate I, fig. 4.) 
Syn. Zygoceros bhombus. Ehr. Ber. Acad. Proc, 1839, p. 156, and 
Trans., 1840, t. iv, f. 11; Bailey, Sil. Jour., 1844, vol. xlvi, 
t. iii, f. 10, 11; Kiitz. Bad, 1844, t. xviii, f. 0, and Spec. 
Alg., p. 139 ; Pritchard, Inf., 1852, p. 450 ; Roper, Mic. 
Trans., 1854, vol. ii, t. vi, f. 5. 
Denticella rhombus. Ehr. Ber. Ac. Proc, 1844, p. 79 ; Pritch. 
Inf., 1852, p. 345. 
Odontella rhombus. Kiitz. Spec. Alg., 1844, p. 136. 
Zygoceros radiatus. Bail. Notes, 1853, t. i, f. 29. 
Biddulphia rhombus. W. Smith, 1856, Syn., vol. ii, t. xlv and 
Ixi, f. 320. 
This fine species is not so common as the preceding, 
though it is by no means rare in the Thames. The finest 
and most abundant collection, however, that I have seen, 
occurs in the clay obtained by Mr. Okeden from a 
brickyard near Caermarthen. I know of no foreign localities 
in which it has been observed, excepting those noticed by 
Ehrenberg in the North Sea and Baltic, and in North 
America by Professor Bailey. The structure of the valves in 
this, as in all the following species, diff'ers from those which 
♦ Ag., ♦ Consp. Crit. Diat.,' p. 56. 
