BRITISH PEARL-MUSSEL. 'Unio margariti/erun. 



CHINESE PEARL-MUSSEL. Hipsas plicutw 



by the presence of the foreign body forces the mollusc to deposit the nacreous secretion 

 upon the intruding substances, and after a while the shot are covered with layer upon 

 layer of pearly substance, the thickness of the coating depending upon the length of time 

 occupied in the construction. 



The same ingenious people are also accustomed to make curious little pearl-covered 

 josses, by stamping them out in thin bell-metal, slipping them into the shell, and leaving 

 them between the valves until they are sufficiently coated with pearl. The example from 

 which the illustration was taken is in Mr. Cuining's collection together with several 

 others. 



IN the THOKNY CLAM, a curious member of another family, the shell is covered with 

 long and branching projections, something like the horns of a young roebuck. All the 

 Clams are natives of the warmer and tropical seas, especially among coral reefs, and their 

 colour and shape are extremely variable. Mr. Broderip writes of them as follows : " The 

 shells are attached by their external surface to submarine bodies, such as coral rocks, and 

 shells have been observed at depths varying from points near the surface to seventeen 

 fathoms. These shells appear to be subject to every change of shape, and often of colour, 

 that the accidents of their position may bring upon them. Their shape is usually 

 determined by the body to which they are fixed ; and the development of the foliated 

 laminae which form their general characteristic is effected by their situation ; and their 

 colour most probably by their food, and their greater or less exposure to light. The 

 Chama that has lived in deep and placid waters will generally be found with its 

 foliations in the highest state of luxuriancy, while those of an individual that has borne 



