given by Mr. Shadbolt in the Transactions of the Microscopical Society
of London, vol. iii. p. 49.
1. Arachnoidiscus Ehrenbergii, Bail. Pseudo-nodule surrounded
with a double row of puncta, the interior linear, the exterior circular.
Diam. '0051" to ’Oiei". v.s.
A. Ehrenlergii, Bail, sic cl. De Brebisson in lit. cum icone photographicâ
pulcherrimà ! A. Japonicus, Prit. Anim. xxiv. 18-21.
Marine. Ilfracombe, Mr. Ralfs.
Supp. Plate XXXI. 256.
Genus 10. TRICERATIUM, Ehr.
Frustules free or attached, triangular ; valves cellular, angles elevated
or produced.
The triangular form of the frustules separates this genus from all
its allies, from which it is also distinguished by the absence of a
pseudo-nodule, the appearance of such in T. striolatum ? being probably
accidental in the single individual from which the figure was
drawn. The frustules are probably at first attached to larger Algæ,
but I have been unable to determine this point from the isolated specimens
which have fallen under my notice. The species hitherto
found in Britain have occurred on the southern and eastern coasts, in
the mud of tidal rivers.
1 . Triceratium Favus, Ehr. Cells hexagonal, angles produced into
horn-like obtuse processes, v.s.
Kütz. Bacill. xviii. 11. Quek. H. C. xü. 22 a. Bail. Sound, fig. 54. Prit.
Anim. xiv. 43, 44.
Marine or brackish water. Thames near Faversham, Mr. Shadholt. River
Orwell near Ipswich, Mr. Hodgson. (Near Charlestown, communicated by
Prof. Williamson.)
Plate Y. 44. Supp. Plate XXX. 44.
2. Triceratium altemaus. Bail. Cells circular, angles slightly
elevated, v.s.
Bail. Sound, figs. 55, 56.
Marine. Poole Bay, Aug. 1848. Hove, Sussex, Nov. 1852 very sparingly,
W. Sm. Folkestone, Sept. 1852, Mr. Capron. (Peruvian Guano.)
Plate V. 45. Supp. Plate XXX. 45.
3 Triceratium striolatum ? Ehr. V. with acute angles, not ele-
' vated or produced ; cellular structure faintly discernible, v.s.
Kütz. Bacill. xvüi. 10?
Brackish water. Near Lewes, Oct. 1850 W. Sm. I refer this doubtfully
to the species described and figured by Prof. Kutzing.
Plate V. 46.
Genus 11. CYCLOTELLA, Kütz.
Frustules free or adherent, disciform ; valves convex or plane, striated,
striæ rajæd.
Closely allied to Coscinodiscus and Melosira, the absence of a cellular
structure separating it from the first, the shaUow valve and nonadherent
frustule from the second. The undulations on the F.V. of
the species first described, which are by no means constant, are
probably due to an irregular depression in the centre of the valve, a
character which may he also noticed in the second species, but being
less strongly marked in the latter, and the outline being more regular,
the appearance of undulations is not so evident. I have also noticed
in the first species, that although no undulations may be discernible
in the dry frustule, they become apparent when the objects are immersed
in balsam.
1 . Cyclotella Kutzingiana, Thw. V. undulated; striæ delicate,
extending over half the disc, at margin 20 in -OOl" ; centre of V.
smooth. Diam. -0005" to 0015". v.v.
¡0. Valve without undulations.
Thw. Ann. 2nd Ser. vol. i. pi. xi. n. C opercnlataji. rectajula Kütz. Sp.
Als. p. 19- ad specimina qiiæ inisit cl. De Brebisson, Oct. lHo2.
Fresh or brackish water. Near Bristol, Ur. Tlmaites. Nov.
1848. /3. Lewes, Oct. 1850, W. Sm. Thames, Northfleet, Mr. Shadholt,
Feb. 1851.
Plate V. 47. h', Sporangial (?) frustule.
tispiecc, fig. XLVII.
Frustule with endochrome, Fron