G e n u s 7- EUPODISCUS, Ehr.
Frustules free or
elevated processes
r adherent, disciform ; valves convex ; disc with
5SPS.
Closely allied to the last, but differing from it in the less distinctly
cellular structure of the valve, which in some species is wholly absent,
and in the presence of the horn-like processes of the disc, which do
not occur in Coscinodiscus. It differs from Genus 10. in its orbicular
form and in the horns springing directly from the surface of the valve,
while in Triceratium they are confined to the angles and are formed
by the prolongation of the latter.
1 . Eupodiscus Argus, Ehr. Cells of V. irregular in outline, processes
three or four. Diam.-0065" t o ’Oils", v.s.
Kiitz. Bacill. i. 6. E. Germanieus, Kiitz. Sp. Alg. p. 134. Prit. Anim.
xiv. 41.
Marine or brackish water. Thames near Gravesend, Mr. Poulton. Near
Faversham, Mr. Shadbolt. River Orwell near Ipswich, Mr. Hodgson.
Plate IV. 39.
2. Eupodiscus fulvus, n. sp. Cellular structure indistinct, radiate ;
colour of dry valve tawny. Diam. '0018" to ’0028". v.v.
Marine. Poole Bay, Sept. 1851, W. Sm.
Plate IV. 40.
3. Eupodiscus crassus, n. sp. Cells circular; V. somewhat opaque ;
colour of dry V. purplish ; margin smooth. Diam. -0011 to ’0021.
v.v.
Marine. Poole Bay, 1848, TF. Sm. Near Ipswich, Mr. Hodgson.
Plate lAh 41.
4. Eupodiscus radiatus. Bail.} Cellular structure of V. distinct;
cells circular ; processes four, radiate, two larger than the others,
v.s.
Marine. Detected by Mr. TFest among other Diatomaceæ from the rivers
Orwell and Thames.
Supp. Plate XXX. 255.
5. Eupodiscus sculptus, n. sp. V . striated, the central striæ forming
a quatrefoil; processes two. Diam. -OOlS'' to -0025". v.s.
Marine. Poole Bay, Sept. 1851, TF. Sm.
Plate IV. 42.
G e n u s 8 . ACTINOCYCLUS, Ehr.
FruMules free or adherent, disciform; valves cellular, undulated;
pseudo-nodule central, conspicuous.
The undulations on the surface of the valves appear on the side
view as radiating bands ; on the front view their true character is
easily seen, and they at once distinguish this genus from its allies.
I t may also he noticed that the cellular structure of the disc is absent
from a small portion (pseudo-nodule) in the centre of the valve.
1. Actiuocyclus uudulatus, Kütz. Valve with six rays. Diam-
•0009" to -0040". v.v.
Kiitz. Bacill. i. 24.
Marine or brackisR water ; frequent. Poole Bay, Sept. 1849. Near Lewes,
Sept. 1850, W. Sm. Near Ipswich, Mr. Hodgson. (Peruvian Huano ; Kicii-
mond, Virginia.)
Plate V. 43.
Genus 9. ARACHNOIDISCUS, Bail.
Frustules adherent, disciform; valves plane or slightly convex, cellular,
marked with concentric and radiating lines; pseudo-nodule
central, conspicuous.
This beautiful genus was, I believe, established by Professor Bailey
of New York, and has been found in abundance upon Algm collected
in Japan, California and South Africa. The discovery of its British
habitat is due to M. De Brebisson of Falaise, who detected a single
frustule of the species described below on Sphacelaria olivácea, Ag.,
collected by Mr. Ralfs at Ilfracombe in North Devon. A minute
description of this species with carefully executed figures has been