Roper, on the DiatomacecB of the Thames. 67 
Some Observations on the Diatomace^ of the Thames. By 
F. C. S. Roper, F.G.S. (Read January 25th, 1854.) 
In the year 1843 M. Ehrenberg, read before the Academy of 
Sciences of Berlin a paper on the microscopical marine infu- 
soria of the deposits of the Elbe,* in which he established the 
remarkable fact that at Gliickstadt, a distance of forty miles, 
and even above Hamburg, upwards of eighty miles, from the 
mouth of the river, marine siliceous-shelled Infusoria were 
found alive, and their skeletons deposited in such abundance 
in the mud of the river, that at the former locality they form 
one quarter to one-third of the entire mass, and that the pro- 
portion is still about half that amount at Hamburg, as far as 
the flood-tide extends. All his observations gave a great pre- 
dominance of marine over fresh-water species, even when the 
salt taste of the water was no longer perceptible. 
In the lists which accompany this paper, M. Ehrenberg 
enumerates thirty- four marine species, under the style of 
siliceous-shelled Polygastrica^ the whole of which would now 
be classed as Algce, under the order Diatomacece. The local 
distribution of these organisms is a point of some interest ; and 
as well-authenticated lists of species from the different localities 
in Great Britain have still been only partially attempted, I am 
induced to lay before the Society the results of some observa- 
tions on the deposits of the river Thames, which accord in a 
great degree with those made by Ehrenberg in the Elbe, 
though the proportion of marine to fresh-water species is more 
equal at corresponding distances from the sea. 
The abundance of the Diatomacece, and the facility with 
which the different species have been collected at Hull, 
Poole Harbour, and other well-known localities, where they 
may be gathered alive, and offer such advantages for acquiring 
an intimate acquaintance with their habits and modes of 
growth, has tended, in a great measure, to divert attention 
from those which are deposited by the Thames water ; and, 
with the exception of some species of Triceratium, JEupo- 
discus, and a few other forms, the greater part of the list I 
shall hereafter mention has been hitherto, so far as I am 
aware, altogether unnoticed, or at all events no special detail 
of them has been given from that locality. 
The chief cause, I imagine, for this neglect of the Diato- 
macece of the Thames and other rivers, has arisen from the 
fact, that observers have endeavoured to pursue the same plan 
* Verhandl. der Konigl. Preiiss. Akad. der Wissenschaften zu Berlin, 
1843. 
VOL. II. h 
