8a 
Okeden, on Diatomaceae. 
above two hundred and thirty species, many of which are 
either new or interesting varieties of known species, which, 
from having such an embarras des richesses, I have been 
able to collect a tolerable number of the more known species 
in a very fair state of purity. 
With a very few exceptions, the whole of these genera and 
species are contained in the accompanying slides which I 
have now the honour of laying before you, and which I beg 
the Society to accept, if they think them worth adding to 
their cabinet. The cabinet in which they are contained is 
one I designed some time ago for the purposes of travelling, 
and which I have found extremely convenient, as it holds 
a large number of slides (228) in a small compass, and re- 
quires no packing ; the mere shutting of it up keeps every 
slide in place, while, from their arrangement, every label can 
be read, and each slide easily got at. Its economy is no 
small recommendation, the cost being only fifteen shillings. 
Accompanying it, I beg to hand in two documents ; one is 
a catalogue of the slides and their contents, the slides being 
numbered to correspond; the other is an alphabetical cata- 
logue of the genera and species; and opposite each species 
is the number of the slide in which it is to be found. Where 
the same species occurs in more than one slide, the best 
sample of it is shown by underlining the number of the slide 
in which it occurs. 
Where I have thought it necessary, I have mounted a slide 
dry as well as in balsam ; and most of the filamentous spe- 
cies I have mounted so as to show them in their natural 
state, unboiled in acid. This has been done by burning out 
the endochrome of the living plant, and then mounting in 
balsam in the usual way. This will be found a very good 
plan for these species, and I would cite Nos. 66, 42, 62, and 
89, as a sample. 
In order to render the habitats more distinct, labels of 
different colours are used, thus : 
Fresh -water . . . ^Yhite. 
Brackish .... Dark yellow. 
Marine .... Light yellow. 
Clay-borings'^ . . . Pink. 
Of course I am not going to weary you by a recapitula- 
tion of the whole of the genera and species in the catalogue, 
but I would wish to call your attention to a few of those 
which are of the most interest, as being either new — I mean 
* Clay-borings are numbered separately. 
