480 PROFESSOR GREGORY ON 
line, and leaving a very small, round, blank space in the centre. Central nodule 
indefinite. The F.V. has not yet been recognised. 
This form is remarkable for the shape of the S.V., which is that usually found 
in the F.V. It occurs rather sparingly in Professor ALLMAN’s dredging from Lam- 
lash Bay, which, of all the dredgings, is the richest in species, whether known or 
undescribed. 
8. Navicula nebulosa, n. sp. Pl. IX., fig. 8. Form oval, broad; generally with 
a slight tendency to angularity in the middle, and also a tendency to acumina- 
tion at the apices. Length from 0-0025” to 0°0035"; breadth 0:0013" to 00016". 
Median line sharp, ending in two elongated expansions at the centre, which do 
not meet. Nodlue indefinite. On each side of, and close to, the median line, is 
a narrow rectangular band of striation, interrupted at the nodule. At the margin 
is a somewhat broader, but still narrow, striated band, almost exactly of uniform 
width throughout. Strize 34 to 36 in 0-001". Aspect of valve hazy and indistinct. 
Striated portions pale blue under the half-inch objective. This form is allied to NV. 
Hennedyji, figured in my second paper on the Glenshira sand (see Trans. Mic. Soc., 
vol. iv., pl. v., fig. 3.) But I have found it necessary to separate it from that spe- 
cies, in consequence of its very different aspect. V. nebalosa is a smaller form than 
N. Hennedyi, the one here figured being an unusually large one. It is also much 
more finely striated; and, above all, it has invariably that peculiar indistinctness 
of aspect from which I have named it; whereas NV. Hennedyi, even when of a 
smaller size, as we sometimes find it, is always remarkable for the sharpness of 
its markings. The tendency to angularity generally seen in WV. nebulosa is never 
found in NV. Hennedyi. Lastly, the striation of the former is so much finer, that 
the striated parts, seen under a low power, have a very pale bluish tinge never 
seen in the latter. When the two forms are seen in the same field of view, as often 
happens in Professor ALLMAn’s dredging from Lamlash Bay, and even when N. 
Hennedyi is the smaller, though it is generally much larger, the difference between 
them is very striking. I might have considered NV. nebulosa as a variety of N. Hen- 
nedyi, but that I have found both forms exceedingly uniform in their characters, 
and have not been able to observe any tendency to transition from one to the other. 
N. nebulosa is frequent in the Lamlash Bay dredging just mentioned, in which WV. 
Hennedyi also occurs; but elsewhere I have hardly ever seen the present species. 
9. Navicula Barclayana, n. sp. P1.1X., fig.9. Form an elongated oval, some- 
what suddenly contracted to acute extremities, terminated by small round api- 
culi. Median line narrow, ending at the middle in two small expansions. No- 
dule indefinite. Length 0:004" to 0:0045”; breadth 0.001” to 0:0012". Striz 
about 38 in 0-001”, somewhat inclined, sharp, minutely moniliform, confined toa 
marginal band, which is rather narrow, and of uniform width except near the 
apices, where it becomes narrower. 
This is a fine conspicuous form, and occurs not unfrequently in the same Loch 
