38 
Wallich^ on Siliceous Organisms. 
so complete is the solvent action of the Salpean stomach, 
that, although protected by their siliceous shell, the cell-con- 
tents are, at times, so completely removed as to give the 
frustules the appearance of having been subjected to boiling 
acids. When we take into consideration then the enormous 
destruction and renewal of these microscopic organisms that 
must constantly be going on, in order to provide food for the 
vast assemblages of Salpse referred to; and, further, when 
we reflect that the Salpse and other molluscoid creatures con- 
stitute in turn the almost entire source of food to the gigantic 
Cetaceans of the same seas, we are surely warranted in as- 
suming that a powerful influence must be exercised on the 
deep-sea deposits by the exuviae derived from these combined 
causes. 
I shall now proceed to describe some of the most interest- 
ing forms of Diatomacese, alluding but cursorily to such 
minor forms as only deserve notice from their frequent occur- 
rence or simple novelty; and reserving for fature notice 
a large number of highly curious mixed forms, which it would 
be impossible to embrace within the limits of this paper with- 
out omitting the last portion of my subject, namely, the rela- 
tion that appears to exist between the siliceous material 
referred to and the nodular flints of the Chalk. 
CosciNODiscus, Ehr. 
C. Sol, n. sp. — Valvular disc surrounded by a broad mem- 
branous ring, the surface of which presents numerous radiating 
lines. Valve precisely as in C. radiatus. 
Total diameter '0016 to '0050; diameter of central portion 
•0020 to -0025. PI. II, figs. 1, 2. 
From Salpse, Bay of Bengal and Indian Ocean. April, 
1847. 
The remarkable appendage to the valvular disc at once 
serves to distinguish this beautiful diatom from all its allies. 
Indeed, at first sight, it presents us with so anomalous-look- 
ing a feature, as to render it doubtful whether it ought to be 
referred to the genus indicated. I shall show, however, that 
the membranous appendage is, after all, but a modification of 
structure found in other forms, and that the central disc is so 
identical in character with the well-known species, C. eccentri- 
cus as to leave no room for question. 
On subjecting the frustule to acids, the membranous ring 
is at first simply detached ; after a while it is dissolved, and 
the central disc then becomes indistinguishable from small 
valves of C. eccentricus. The ring is hyaline, and free from 
