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 off. 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 UNIO MARGARITIFERA 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 

 structure 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 VL 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- 

 cies. 



The flesh must be extracted from the large claws of Lob- 



