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CENTROP0RUS. 449
ANALYSIS OF SPECIES.
Valve apparently divided into compartments, striation very distinct . H. stelliger.
Valve not divided into compartments, striation extremely delicate .
H. subtilis.
H. subtilis Bail. (New spec, 1854, p. 10, f. 12; CI. and Moll.
Diat., No. 2, sub. H. Franklini E.)
Valve orbicular, convex, not apparently divided into compartments ;
umbilicus, very distinct, coarsely punctate, with irregular, jagged margins.
Valve apart from the umbilicus, apparently hyaline, with very delicate
structure, puncta in lines crossing one another, forming 24 to 26 striae in
1 c.d.m. at the median part of the valve, and attaining as much as 30 at the
extreme marginal portion. Diameter, 2 to 10 c.d.m.
Marine. Authors have not recorded the large form from our regions, but I have found rare
specimens, possibly reaching there accidentally, not only on the Belgian coast (Blankenberghe),
but also in the mud of the Scheldt. The smaller form inhabits our country, and has been
recorded from Scotland, North Wales (Stolterfoth), and has been described under the name of
H. scoticus [Kiitz] Grun. ! (= Cyclotella Scotica Kivtz. in Coll. H.V.H. H.V.H. ; Atl., pi. 84,
f. 15-18*), plate 35, fig. 917 (
: 600).
H. Stelliger Bail. (New Spec, 1854, p. 10; Podosira maculata
IV. S/n. ; H.V.H. Atl , pi. 84, f. 1,2*; Type No. 454), plate 22, fig. 650.
Valve orbicular, apparently divided into a large number of compartments.
Umbilicus very distinct, finely granular, with irregular margins often laciniate,
prolonged so as to form the margins of the compartments. Valve with
granules arranged in quincunx, forming about 16 lines in 1 c.d.m. Diameter,
3-5 to 8-5 c.d.m.
Marine. Frequent : Blankenberghe, Ostend, Heyst, Antwerp (Scheldt). : England
Surface of Dee, ; (Stolt.)
Hull
(Kitton);
on all the coasts of the North Sea.
Norfolk,
(H.V.H., Type No. 529). Bahnsea. Probably found
GENUS 115 CENTROPORUS PANT., 1889.
Fig. 174. Centroporus crass its.
Valves convex, orbicular, with broad
margin
decorated with small arcuate
compartments, striolate and separated
from the disc by a hyaline annulus.
Disc punctate, with fine puncta arranged
in radiant rows, centre rounded, with-
out puncta.
found in a fossil state at Ananino in Russia.
This genus only comprises a single
form, C. crassus Pant., which we reproduce
here (fig. 174), and which has been
v F