LDiatoms. 333 
water for half an hour, which will kill the animalcule at- 
tached; and when the weeds are rubbed and stirred about 
in the water, they come off and form a cloud of muddiness, 
which is to be allowed to settle, and the water then poured 
off and the sediment transferred to an oil flask (which has 
been well cleaned), and boiled with nitric acid over a candle 
or gas jet. After the first portion of the acid ceases to act, 
the flask, with its contents, must be set aside till the liquid 
is perfectly clear, when it is to be poured off, and fresh acid 
added. This is to be continued as long as the acid exerts 
any action, and the sediment is perfectly white, when it is 
to be washed with water until the liquid is no longer acid. 
In this sediment, when examined by the microscope, 
may be found the 77zceratium favus, which is one of the 
largest of the Diatomacez, and is about the 1-16oth of 
an inch.in diameter, It is in the form of an equilateral 
triangle, with slightly curved sides. At each corner is a 
projecting spine or hook, and round the base of each there 
isa tow of round dots; and the rest of the surface is 
covered with large and regular hexagonal markings, resem- 
bling, in the closest manner, the formation of honey-comb. 
If you wish to mount it, when found, you must pick it out 
from among the grains of sand and other impurities by the 
help of a stout hair from a shaving brush, or a cat’s 
whisker stuck in a split at the end of a slender wooden 
handle, such as a paint-brush handle, and place it in the 
centre of a glass slide. A drop of Canada balsam is then 
to be added, and the slide warmed till the balsam becomes 
rather hard. On cooling, all the air-bubbles should be 
broken by the point of a needle, and then the thin glass 
cover is to be put on, taking care to have the object as 
nearly in the centre as possible, and not to press so hard 
as to break it. Objects mounted in this way, under small 
round pieces of thin glass, on plain ground edged slides, 
look very neat; and all the rest of the things described in 
this paper may be mounted in the same way, though more 
than one specimen may be mounted at once. Suwurzrella 
constricta, which resembles a lady’s needle-case, may also 
be found. It has strongly-marked ribs running from the 
outside edge towards the centre, where a clear space may 
be observed. Surirella plicata has no resemblance to the 
last; but strongly resembles a lemon in outline, as does 
also another object (of which I never found but one), but 
which is covered with minute dots instead of being marked 
with faint lines. A small, but beautiful variety of the 
