ill!Ill

2T4
NAVICULA.
Valve very elongate, linear, gently inflated at the median portion and at the
apices; raphe not surrounded by a hyaline area; longitudinal
and transverse
stria? delicate, cutting one another at right angles, equally distant, about 20 in
1 c.d.rn. Length, 13 to 14 c.d.m. Breadth at the median portion, 1 c.d m.
Brackish water. Not yet found in Belgium. England, Ireland, France.
var. Belgica H.V.H. (H.V.H. Atl. Supp., f. 29*), plate 4, fig. 189.
Much smaller than the type form and with very pronounced inflations.
24 striae in 1 c.d.m. Length, 6 to 7 c.d.m. Breadth at the central
inflation, 075 c.d.m.
Brackish water. Ostend (Charles Petit).
XIII. Crassinerves.
{ Valve lanceolate, with apices not rostrate-capitate . . N.
cuspidata.
-{ Valve with apices rostrate-subcapitate *. N. ambigua.
(. Valve rostrate-subcapitate, showing transverse thickenings . . forma
craticula.
N. CUSpidata KlltZ. (Baa, p. 94, pi. 11, f. 24 and 37; H.V.H.
Atl., pi. 12, f. 4*), plate 4, fig. 190.
Valve broadly lanceolate, with apices gently inflated, not rostrate ; trans-
verse striae gently radiate, almost perpendicular to raphe, fine, reaching
almost to the raphe, 14 in 1 c.d.m. Longitudinal striae fine and more
compact. Length, about 9 c.d.m. Breadth, 2-3 c.d.m.
Fresh water. Common throughout Europe.
var. halophila Grun. (H.V.H. Atl. Supp., f. 30*; in Type No. 12),
plate 4, fig. 191.
Narrow, very small: about 5 c.d.m.; striae delicate, about 16 in 1
c.d.m., radiate near the median portion, convergent at apices.
Brackish water. Blankenberghe.
N. ambigua Ehr, (Amer., 1843, p. 129, pi. II. 2, f. 9; H.V.H.
Atl., pi. 12, f. 5*; Type No. 121), plate 4, fig. 192.
Differs from the preceding, of which it is probably only a variety, by its
smaller size, and its apices which are rostrate-capitate. Length, 6 to 7 c.d.m.
Breadth, 1*5 c.d.m.
Fresh water. Common throughout Europe.
forma craticula. (H.V.H. Atl., pi. 12, f. 6*; Type No. 122), plate
4> fig- 193-
Valve showing transverse thickenings.