Diatomaceous Sand of Glensliira, 
47 
paper, and which has yielded so many fine new forms, a still 
larger and finer JVavicula, to which he has paid me the com- 
pliment of attaching my name. In this form also, we find 
the projecting, rounded, club-like snouts to the valve, standing- 
out from it in the same manner. It is quite distinct from the 
form here figured, although, no doubt, the two forms belong 
to the same group. I think I have seen, in the Glensliira 
Sand, indications of a tendency in the larger forms of Navicula 
Smithii, Breb. {elliptica, Sm.), to pass into snouted varieties, 
with the snout rising in relief from the surface of the valve. 
1 have not met with N. clavata^ except in this deposit. (273.) 
18. Pinnularia longa^ n. sp. This remarkable form, of 
which an average example is represented in fig. 18, is not 
rare in the deposit, but, on account of its slenderness, is 
seldom found entire. 
Form rhombic, very long and narrow, with acute termina- 
tions. Costce very conspicuous, distant, inclined or radiate, 
about 12 in 0 001". Length from 0-004" to 0-008", but 
usually about 0*006". The only known form to which it has 
any resemblance is P. directa, Sm. But in P. directa, the 
form is rather lanceolate than rhombic, while the striae are 
much more numerous, and are also parallel, reaching the 
median line, which those of P. longa^ in the middle, at least, 
do not reach. Moreover, P. directa^ so far as I have seen, is 
a much smaller form. P. longa has another peculiarity, 
which is, that the median line, as seen in the figure, is gene- 
rally twisted. The valve appears very thick. (274.) 
19. Pinnularia fortis^ n. sp. This is a very pretty little 
form, and frequent in the lighter densities of the deposit. It 
is well represented in fig. 19. 
Form nearly rhombic, or rhombic lanceolate, rather short, 
apices somewhat obtuse. Length from 0-002" to 0-0035. 
Costae conspicuous, about 16 in '001, and apparently projecting 
from the surface of the valve, for on the edge view they seem 
to stand out, and the valve has, in consequence, a very pe- 
culiar aspect. The valve is also very convex towards the 
extremities, but concave in the middle, which gives to the 
F. V. a constricted form. There is a blank space at the 
centre, round which the costse radiate. There is something 
about the form very difficult to reproduce in a drawing. 
The costse appear very distant, yet when counted, we find 
them much more numerous than we expected ; and if we 
give in the figure the real number, the whole character of 
the form is lost. This character is well represented in the 
figure, but there are fewer costse there than in the original. 
It is a very well-marked form. (275.) 
