64 NAVICULE. 
constricted in the middle, angles prominent, extremi- 
ties truncate. V. linear-lanceolate or linear-elliptical, 
with rounded extremities; striz oblique, granular, 
distinct, 25 in ‘001", reaching to the median line, 
much shortened (so as to leave an imperfectly orbi- 
cular blank space) around the central nodule ; colour 
of dry valve bluish green. 
This species differs from N. aspera in the colour, outline, 
and much greater convexity of the valve, in the finer strie 
and the orbicular shape of the blank space around the cen- 
tral nodule, in the angles of the frustule on M. V. being pro- 
minent and sharp, and the middle more deeply constricted ; 
it differs also in its habitat, which is the sandy beach. 
Hab. Marine: in sand-gatherings frequent, and occa- 
sionally quite pure and abundant. Cresswell, Boulmar, 
Newbiggin, and Tynemouth sands, Northumberland, South- 
Shields sands, Durham (4. S. D.). 
D. Valve linear, with rounded extremities ; striae coarse and costate. 
* Not inflated in the middle. 
Navicula retusa, De Brébisson. 
Naviula retusa, Bréb. Diat. de Cherb. p. 16, fig.6; Sm. Synop. vol. ii. 
p. 92; Ralfs, in Prit. Inf. p. 908; Donk. in Quart. Micr. Journ. 
ns. Vol.i. p. 14, pli. fig.17; Rabenh. Europ. Diat. p. 186. 
Navicula pectinalis, Bréb. Sm. Synop. vol. ii. p. 91; Ralfs, in Prit. Inf. 
p. 909; Rabenh. Europ. Diat. p. 186. 
Plate X. figs. 3a & 3. 
Frustule small, on M. V. oblong, constricted in the middle, 
angles rounded, extremities truncate. V. narrow, 
linear, with rounded extremities ; stria not reaching 
to the median line, nearly transverse, distant, coarse, 
and costate, 20 in ‘O01". 
