ill!Ill

NAVICULA. 189
IV. All the Stria: perpendicular to the raphe.
N. directa W. Sm. ! (S.B.D., i., f. p. 56, pi. 18, 172*; sub
Pinnularia ; in Type No. 394) ; plate 25, fig. 722.
Valve linear-lanceolate, infinitesimally attenuate up to the acute apices.
Striae about 7 in 1 c.d.m., exactly perpendicular to the raphe, which they
almost touch. Length, 6 to 9 c.d.m.
Marine. England (W. Sm. !). Scotland (W. Arn. !). Ireland (O'Meara). This diatom is
not common, but will certainly be found in other parts of the North Sea.
var. subtilis. {Finn, subtilis Greg., Clyde, p. 488, pi. 9, f. 19*) ; plate
25> fi g- 7 2 3-
More rhomboidal and at the apices more acute than the type form ; 9
or 10 delicate costae in 1 c.d.m.
Marine Ccast of Scotland (Lamlash Bay, Greg. 1.
N. Northumbrica Donk. (Q.J. M.S., 1861., i., n.s., p. 9., pi. 1.,
t. 5 ; id., Brit. Diat, p. 54, pi. 8, f. 1* ; in H.V.H.'s Types oi Syn., Nos. 13,
116, and 369) ; plate 25, fig. 726.
Valves narrowly lanceolate, with apices attenuate-acute. Striae about
7 or 8 in 1 c.d.m., very delicate and perpendicular to the raphe,
the median
somewhat coarser and more distant. Central nodule opaque, very con-
spicuous. Girdle face very broad, subquadrangular, somewhat concave from
the sides of the valve. Length of valve, about 5^5 to 6-5 c.d.m. Breadth,
somewhat more than 1 c.d.m.
Marine. England, Ireland, France.
B. Terminal nodules distant from the apices of the valve.
1. Valve with equal sides.
N. superimposita Ad. Schm. (Nordsee, p. 90, pi. 2, f. 34*),
plate 25, fig. 724.
Valve lanceolate or sublanceolate, with apices rounded, more or less
capitate, with longitudinal median portion considerably super-elevated, in such
a manner as to simulate a second smaller valve placed on the lower. Striae
robust, radiant, shortened, 4 or 5 in 1 c.d.m., not reaching to the raphe, and
leaving a considerable stauroform hyaline space round the central nodule.
Length, 9*5 to 11*5 c.d.m.
Marine. North Sea (Hvidingsoe, A. Schm.).