IX] PEARLS IN JE^YELLERY, ETC. 123 



Cassis tuherosa Linn., Cassis cornnta Linn., and the 

 " conch " sliell of the West Indies—Strombus glgas 

 Linn. The latter is a very large shell but is not so 

 valuable as the others. Large quantities were in 

 former days imported into Liverpool from the Ba- 

 hamas, but the writer can get no evidence of the 

 continuation of this traffic. The manufacture of 

 cameos consists in carving away certain of the sur- 

 face layers of the shell. The deeper layers are 

 diiFerently coloured. Consequently an engraving 

 results, in which the picture stands out on a back- 

 ground of another colour. In the case of the conch 

 shell, the cameo is yellow on a beautiful red. The 

 Cassis shells give white on an orange or golden 

 background. 



It may be surprising to most readers of this little 

 book to hear that pearl-like structures occur some- 

 times in plants. It may be quite incorrect to speak 

 of them as pearls, but some of them, especially rare 

 specimens from the cocoanut, are said to resemble in 

 colour and appearance the real pearls from the sea. 



It appears, however, most difficult to get any con- 

 clusive evidence about these calcareous concretions. 



Riedel (according to Professor Korschelt) is sup- 

 posed to have found one of these in a cocoanut in 

 1886 whilst in North Celebes. It was pear shaped 

 and 28 mm. long. Harley, who made chemical analyses 

 of the real pearls, examined a supposed vegetable 



