ill!Ill

NAVICULA. T 75
B. Striation interrupted by a marginal sulcus.
N. blanda Ad. Schm. (Nordsee, p. 90, pi. 2, f. 27*; Pinnularia
Ergadensis Greg., T.M.S., 1856, p. 48, p. 5, f. 22 ?) plate 25, fig. 707.
Valves linear, with parallel or subparallel costae, apices rounded, leaving a
considerable hyaline area round the central nodule and not reaching to the
raphe, feebly radiant in the centre of the valve and somewhat convergent at
the apices, 8 to 10 in 1 c.d.m., interrupted by a very conspicuous marginal
sulcus. Length, 5 to 13 c.d.m. Breadth,
Marine. North Sea, Hvidingsoe (Ad. Schm.)
1 to 2 c.d.m.
N. blanda which has been found in various regions of the globe appears to
be very rare in the North Sea ;
it belongs to a small group of forms of which
N. Poivellii (not yet found on our shores) is the type form.
N. sejuncta Ad. Sch .
25, fig. 708.
(Nordsee, p. 87, pi. 1, f. 18*) plate
This species, still imperfectly known, has also been found at Hvidingsoe
but it is equally rare. This form is much smaller than the preceding and the
stria; reach the raphe throughout.
A .
f Terminal stripe in broken lines
Striae
in
continuous
lines.
f
Median
striae
alternately
long
and
short.
Median
stripe not
alternately
long
and
short.
II. Radiosae.
Terminal nodules approximate to apices of valves.
I. Median striae radiate, terminal striae convergent.
a. STRI.E APPROXIMATE.
r
Valve broadly lanceolate, not rostrate-capitate
Valve \ broadly lanceolate, rostrate-capitate
t Valve anceolate, very narrow .....
Median striae equally shortened forming a pseudo-stauros ; striae
near the central nodule almost straight
No false
stauros
Apices not
rostrate-
capitate.
Apices
rostrate-
capitate.
Nodule
surrounded
by a
considerable -{
hyaline area ;
valve broadly | Apices
lanceolate. (_ diminuate-rostrate
N. oblonga
N. peregi\na.
N. salinarum.
N. cincta.
N. gracilis.
Apices not conspicuously
diminuate-rostrate
. N. vulpina.
conspicuously
N. viridula.
lanceolate median striae ; very
radiate .... N. radiosa.
Hyaline area very small ; valve narrowly
Striae
robust.
Striae scarcely visible
f Hyaline area dilated trans-
versely, apices very
robust .
Hyaline area rounded, apices
sub-obtuse
N. cryptocephala.
N. rhynchocepliala
N. gregaria.