( 67 ) 
On the Post-tertiary Diatomaceous Sand of Glenshira. 
Part II. Containing an account of a number of additional 
undescribed species. By William Gregory^ M.I)._,F.R.S.E., 
M.R.I.A., &c. ; Professor of Chemistry in the University 
of Edinburgh. Illustrated by numerous figures drawn from 
Nature, by R. K. Greville, LL.D., F.R.S.E.,, &c., and 
engraved by Tuffen West, Esq. (Plate I.) 
Continued from No. XVI^ p. 48. 
(Eead March 26th, 1856.) 
24. Pleurosigma (?)_,n. sp. This peculiar form, which 
is very scarce in the deposit, I have not ventured to name, 
although it cannot be referred to any of the species in Smith's 
Synopsis, vol. i. 
Form very slightly sigmoid; extremities obtuse. The median 
line, as may be seen in vol. V, PI. I, fig. 24, is central at one end, 
while at the other it seems to approach the margin for a short 
space just before the apex. This appearance is probably due 
to the circumstance that the valve does not in this case lie 
quite flat. There is an elongated oval expansion round the 
nodule, but imperfect ; and I am not sure that this appearance 
may not depend on some injury to the valve. Length about 
0'0053". I have not been able to resolve the striation as yet, 
and I conclude that it is of the finest ; but until I can examine 
several good specimens, the description must be imperfect. 
(281.) 
25. Cocconeis distans, n. sp. This species was described 
in my former paper, but a form of C. Scutellum was by mis- 
take figured for it; I therefore give a figure of it in fig. 25. 
Some, judging from the former erroneous figure, have sup- 
posed it to be only a form of C. Scutellum, but its whole 
aspect is so peculiar, that those who see the form, which is 
not very rare in certain densities, are at once struck with it as 
peculiar. Professor Kelland, without knowing of it at all, at 
once noticed it in some of the deposit which I prepared for 
him. 
Form always a broad and pure oval. Length from 0*0008" 
to O'OOIS". The transverse rows of dots are not above one 
half of the number of those in the largest and coarsest forms 
of C. scutellum, which abounds here in all its forms, and can 
be easily compared with C. distans. These lines, about 9 in 
O'OOl", are also formed of much fewer and larger dots, and 
these dots are all of equal size, except only that those at the 
margin are sometimes smaller. They are so distant, and the 
lines of them so few, that the form ceases to have a striated 
vol. v. a 
