ill!Ill

148
ENCYONEMA.
C. tumida Breb (Cocconema tumidum Brcb. !
p. 6c, 11. 5 ; H.V.H., pi. 2, f. 10*; Type No. 21), plate 1, fig. 42.
in
Kutz Sp. Alg.,
Valves ventricose, with dorsal margin very arcuate, ventral margin
concave, inflated in the middle, apices very produced-rostrate, truncate or
rounded. Raphe very arcuate, surrounded by a rather broad hyaline zone,
very considerably inflated round the central nodule, dilated portion some-
times showing one or two isolated granules ; central nodule generally having
a small furrow across it in the middle ; stria; robust, quite moniliform, 8 to 9
in 1 c.d.m. Length, about 6 c.d.m. Frustule stipitate.
Fresh or slightly brackish water. Antwerp, Louvain, Ostend, etc.
C. Helvetica Kutz. !
Terminal nodules very elongate
pi. 2, f. 15*; Type No. 32); plate 1, fig. 43.
(Baa, p. 79, pi. 6, f. 13; h.v.h. Atl.,
Valve very lanceolate, with dorsal margin rather convex, ventral margin
very slightly concave, almost straight, abruptly inflated in just the middle
portion ; raphe slightly bent,
with curvature inflected at the middle of the
valve towards the ventral margin \ raphe surrounded by a narrow hyaline zone,
slightly inflated near the central nodule ; terminal nodules very long,
form of a coarse inverted comma ; stria; rather well marked,
wise, about 8 to 9 in 1 c.d.m. Mean length about 7 c.d.m.
in the
divided cross-
Fresh water. Very common, and found in all the countries comprised within our radius.
GENUS 3. ENCYONEMA KUTZ., 1833.
Fig. 27. Encyonema prostration (Berk.) Ralfs,