GREVILLE, ON DIATOMACEA. 81 
discoverer,—a well-merited compliment. Mr. Norman had 
also, in 1856, obtained abundant specimens of a Coscinodiscus- 
like Diatom, by washing the mud which adhered to the 
roots and stems of Dutch rushes imported into Hull from Hol- 
land. This last form was doubtfully regarded by competent 
observers as Coscinodiscus subtilis of Ehrenberg; and as the 
question arose, whether the two forms above referred to 
were not identical, I have been necessarily led into an 
examination of the history and characters of C. subtilis. 
The species was first described by Ehrenberg, in his ‘ Essay on 
the Microscopical Organisms of South and North America ;’ 
and the localities he assigns to it are Peru and Vera Cruz. 
But of the two figures which he gives (tab. I, iii, fig. 18, 
and tab. III, vu, fig. 4), the second, that of the Vera Cruz 
form, is accompanied with a mark of doubt; and it must be 
confessed that the figures are most unlike each other. 
Kiitzing, in his ‘ Bacillarien,’ merely repeats Ehrenberg’s sta- 
tions, and adds another representation, which, again, is too 
indefinite to be depended on; nor does he afford any addi- 
tional information in his ‘Species Algarum.’ The late Professor 
Bailey, of New York, however, who was in direct communi- 
cation with Ehrenberg, found in 1850, im various districts in 
the United States, a Coscinodiscus, which he named, without 
hesitation, swbtilis of that author. In the earth of the rice 
fields of Georgia, particularly, he discovered it in vast 
abundance, and expressed his surprise, that it, and a large 
proportion of the forms which accompanied it, were such as 
only inhabit salt or brackish water ; indicating the presence 
of salt water much further up the rivers than it now extends. 
(‘Microscopical Observations made in South Carolina, Georgia, 
and Florida.’) 
Lastly, Ehrenberg, in his ‘ Mikrogeologie’ (1854), extends 
the geographical distribution of the species very consider- 
ably, giving the following list of localities, with a figure to illus- 
trate each: Canton, China, tab. XXXIV, vu, fig. 6. Sicily, 
tab. XXII, fig. 4. Richmond, Virginia, tab. XVIII, fig. 35 ; 
and tab. XX XIII, xvi, fig. 7. Assistance Bay, North Pole, 
tab. XXXV, xxii, fig. 5. South Pole, tab. XX XV, xxii, fig. 5. 
California, tab. XX XITI, xin, fig. 4. It is much to be regretted 
that none of the above-mentioned illustrations are charac- 
teristic ; and they appear, besides, to differ very considerably 
from each other. Nevertheless, we may, I think, assume 
with some confidence, that the American form is the true 
C. subtilis. If we now compare this with the Coscinodiscus 
discovered by Mr. Norman, in the stomach of Ascidians, we 
must admit that, at first sight, the two species greatly 
