NEW FORMS OF MARINE DIATOMACEZ. 487 
Smithii (olim N. elkptica Sm.), because I have always understood the typical WN. 
Smithii to be a form which is very frequent in the Glenshira sand, and occurs also 
in the new materials. It is ofa short, broad, inelegant, oval shape, flat, colourless, 
_ and much less coarsely striated. Neither does it exhibit the longitudinal ridge so 
distinctly. It may be, that the present form, WV. fusca, is the typical one, and the 
other a variety of it; but in my experience I have only seen WN. fusca in the 
gatherings above named, while I observe NV. Smithii in every marine gathering. 
16. Navicula Smithii, var.-y, nitescens. P1.1., fig.16. Form lanceolate, tend- 
_ ing to rhombic, with obtuse ends. Median line straight, nodule definite. Length 
from 0-002” to 00035"; breadth from 0:0009” to 0:0014”. Strize about 16 in 
0-001”, considerably inclined, obscurely moniliform, and of a shining aspect. 
They are traversed by a ridge, which is about half-way from the margin to the 
median line, and has an outline more rhombic than that of the valve. 
This form occurs both in Lamlash Bay and in Loch Fine, and is not at all 
rare in some of the dredgings. It is conspicuous, from its elegant form and shin- 
ing aspect. It is quite colourless under a low power. I have given it as a variety 
of N. Smithii, from a desire to avoid unnecessary multiplication of species. But I 
am inclined to regard it as distinct from that species, from its peculiar form, its 
smaller size, the character of the nodule and median line, and its bright white 
aspect; all of which characters are very constant. 
17. Navicula Smithii, var. 3, suborbicularis. Pl. 1X., fig. 17. Form a short, 
broad oval, or suborbicular. Length 0-002” to 0:0026”; breadth 0-0013” to 
0:0018". Median line bounded by white lines, curving inwards both to the apices 
and to the indefinite nodule. Striation conspicuous, much inclined. Strize 16 or 18 
in 0-001", moniliform. There is a ridge, as in the two preceding forms, traversing 
the strize, and when the striz near the margin are in focus, those between the 
ridge and the median line are very faint. 
This form occurs in Lamlash Bay, and is also tolerably frequent in one Loch 
Fine gathering, in which the preceding form is not found. Its small size, nearly 
round form, and peculiar median line, with the slightly-marked ridge, compared 
to that in the two preceding forms, seem to point it out as distinct; especially as 
it is very constant in its characters. But, for the reasons already stated, I give 
it asa variety. Itis at least a form to be noticed, and to be considered with the 
_ others with a view to a more accurate determination of species than has yet been 
possible, but which, in the progress of observation, we may hope to attain. 
18. Navicula maxima, Greg. Pl. IX., figs. 18, and 186. Form of §.V. linear, 
_ rather narrow, with obtuse ends. Length from 0002” to 0:008”; breadth of S.V. 
_ from 00-0025” to 0-00011"; of F.V. in the larger specimens, 0-0009” in the middle, 
- 000115” at the ends. Striz fine, but distinct, about 52 in 0:091’, parallel, not 
quite reaching the median line, from which, at the centre, they retire, leaving a 
_ pretty large round space. F.V. rectangular but narrowest at the middle, and 
