COLOURS OP SHELLS. 123 



of such shells is small. The greatest observed density 

 was that of a heUx ; the smallest, that of an argonaut. 

 The shell of the janthina, a floating molluscous creature, 

 is among the smallest densities ; the specific gravity of 

 all the land shells examined was greater than that of 

 Carara marble. 



Nor let it be overlooked, that while the moUusca are 

 able to construct, they can also adorn their habitations. 

 The skin of the little artist is full of ropes ; these con- 

 tain colouring fluids, which, penetratino- the calcareous 

 substance before it is hardened, form its various tints. 

 Nor does it appear that these pores occur at random. 

 On the contrary, they are arranged in the skin of the 

 mollusca as regularly as the spots on the leopard, or 

 the stripes on the tiger ; and the uniformity in the 

 patterns of shells, is the consequence of the order in 

 which the pores are placed in the mantle. 



The providence of God is strikingly manifest in the 

 colours of these creatures. The coverings of such as 

 move readily from one situation to another, and are 

 consequently able to choose the places of retreat, are 

 generally varied with brilliant tints. Some exhibit the 

 glowing colours of the rainbow, or those of the finest 

 tulips, while a considerable number appear as if clothed 

 in silver armour, as thev walk under the shades of the 



