70 CRUSTACEA, 
coatings polished down, till the pearlaceous structure becomes 
visible. It has been a common practice to remove the strong 
epidermis of shells by means of strong acids, but this is a 
hazardous and tedious mode of operating. The best method is 
to put the shells into a pan of cold water, with a quantity of 
quicklime, and boil it from two to four hours, according to the 
thickness of the epidermis. The shells afterwards must be | 
gradually cooled, and some strong acid applied to the epider- 
mis, when it will easily peel of. Two hours are sufficient for 
| the common muscle being boiled. The shells are afterwards 
polished with rotten-stone and oil, put on a piece of chamois | 
leather. 
The epidermis of the Unro Marcaritirera is so thick, that 
it requires from four to five hours boiling. After the epidermis 
has been removed, there is beneath it a thick layer of dull 
calcareous matter, which must be started off with a knife or 
other sharp instrument; this requires great labour, but when 
accomplished a fine mother-of-pearl is exhibited, which adds 
an agreeable variety as a specimen. 
Various Turbos and Trochus’s are also deprived of their 
epidermis, and polished with files, sand-paper, pumice-stone, 
&c., till the pearly appearance is obtained ; but all these modes 
are invented for disfiguring rather than improving the shells 
in the eye of the naturalist, and should never be resorted to | 
except where the species is very common, in which case it is 
well enough to do so with one or two specimens to show the 
siructure of the shells. 
After the operation of polishing and washing with acids, a 
little Florence oil should be rubbed over to bring out the co- 
lours and destroy the influence of the acid. 
CLASS VI.—CRUSTACEA. 
In this Class are included Crabs, Lobsters, and their con- | 
geners. These animals are all protected by a coriaceous co- 
vering or shell, which is easily preserved, although there is 
considerable difficulty in preserving the colours of some spe- 
eies. 
The flesh must be extracted from the large claws of Lob. 
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