ill!Ill

202 NAVICULA.
are less marked, and are only apparent with oblique illumination. Length,
up to 6 c.d.m. Breadth, 2*5 c.d.m. Valve excessively delicate, apparently
hyaline under the best dry objectives.
Marine. Very rare? On the sands at the coast at Cresswell and Boulmar (England ;
Curabrae (Scotland, Coll. W. Arnott in Coll., H.V.H.).
Valve with coarse
puncta.
Valve with fine
gent.
V. Lyratae.
f Sulci more or less divergent, equally broad throughout
. . . . . N. Lyra.
Sulci straight or somewhat convergent, much broader
at their median portion than at the N. apices .
Blank space surrounding the raphe, with median
Donkin).
spectabilis.
apices clavate . . . . , N. forcipata.
Central nodule surrounded by a nar-
, ,
f
Blank J
. space ,
r ,
. ,-
puncta; sulci K- row.hyahne area sulci ; not ' J reaching
J surrounding
a
strongly nver- \
conver- rounoing to the ~\
apex of the valve . . N. abr^pta.
jV
j
with median
apices not
clavate.
Central nodule surrounded by a
broad hyaline area ; sulci reaching
almost to the apices . . N. pygmaea.
A. Siricz formed of coarse granules.
N. Lyra Ehr. (KUtz. Baa, p. 94, pi. 28, f. 55; h.v.h. Atl.,
pi. 10, f. 1 and 2*; Type No. no), plate 4, fig. 161.
Valve broadly elliptic, with apices often somewhat diminuate subrostrate.
Raphe surrounded by a narrow hyaline zone, dilated into a stauros round the
central nodule. Striae formed of coarse puncta, about 7 to 9 in 1 c.d.m.,
more and more radiate from the median portion, and interrupted on each side
of the raphe by a sulcus, the bottom of which is generally smooth, but where
the striae continue sometimes more feebly, incurved at the middle where it
rejoins the stauroneiform hyaline space, in such a manner that the entire
smooth spaces have the appearance of a lyre. Length, 11 to 12 c.d.m.
Breadth, about 5 c.d.m.
Marine. Blankenberghe (rare). Found on all the North Sea coasts.
N. spectabilis Greg. (Diat. of Clyde, p. 9, pi. 1, f. 10*), plate
27, fi g- 757-
Probably only a form of the preceding, from which it differs essentially in
that the sulci are at least twice as broad, and are finely dotted.
Marine. Not yet found in Belgium. Scotland, Ireland, France, Sdlsvig, Cuxhaven,
Marstrand.