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286 COCCONEIS.
GENUS 34. COCCONEIS (EHR. 1835), GRUN, 1868.
Valves broadly oval, elliptic or discoid, rarely lanceolate ;
the upper
having only a pseudo-raphe, the lower furnished with nodules and a
a. b. c
Fig. 65.- Cocconeis Scutellum.
a. Upper valve, b. Lower valve, c. Annulus.
true raphe. Frustules arched or genuflexed, living as a parasite on
other algae. Endochrome as in the Achnanthes.
The genus Cocconeis includes numerous and varied species. It has been
skilfully divided by Prof. Cleve into a certain number of groups which may
be considered as subgenera or even as genera if that be preferred. The
following are the groups which I adopt to distinguish my species :
ANALYSIS OF GROUPS.
Valve f Upper valve furnished with distinct costae
having a -1
marginal (, Upper valve punctate, striate .
ring.
Valve
having
neither
interior
skeleton
nor ring.
f Upper
valve
furnished
with
costae.
Upper
valve
without
costae.
f
Valve |
elliptic
|
I
Valve lanceolate
Upper valve with a broad axial area
-\ Upper valve
with narrow -J
axial area. j Valve
f Valve elliptic or broad
linear or lanceolate,
1. Pleuroneis.
2. Cocconeis.
3. Disconeis.
4. Actinoneis.
5. Heteroneis.
6. Eucocconeis.
t I with fine puncta . 7. Microneis.
* Valve having a separate marginal ring.
Group i. Pleuroneis Cleve. Upper valve furnished with distinct
costae.
P. COStata (Greg.) Cleve; (C. Costata Greg., Q.J.M.S. 1855, iii., p. 39,
pi. 3, f. 10 ; H.V.H. Atl., pi. 30, f. 11-12*3 Pleuroneis Costata Cleve in litt.),
plate 29, fig. 816.