228 MOLLUSCA. 



blue, and purple, and at last settles in a fine unchangeable 

 crimson. Neither acids nor alkalis affect its colour, and it 

 may be conveniently employed in marking linen, where an 

 indelible ink is desirable. The Scalaria clathrus (Turbo 

 clathrus of Linnaeus) also furnishes a purple liquor of con- 

 siderable beauty, but it is destructible by acids, and gradu- 

 ally vanishes by the action of light. The Planorbis cor- 

 neus likewise yields a scarlet dye, but of still less perman- 

 ency than the scalaria, as all attempts to fix it have hitherto 

 proved ineffectual. 



We cannot conclude this chapter without remarking, that 

 the study of molluscous animals rises in importance as we 

 perceive its utility. When we are told, that searching for 

 shell-fish, and conveying them to the market, give employ- 

 ment to a British population of upwards of 10,000 ; that 

 these animals furnish nourishing food to innumerable fami- 

 lies, and in years of scarcity prevent the horrors of famine ; 

 we will be disposed to regard with a favourable eye the la- 

 bours of that naturalist who examines the structure and 

 economy of those animals, that, from a knowledge of their 

 nature, he may render them still more subservient to our 

 purposes. 



Even when considered as objects of amusement, mollus- 

 cous animals are not devoid of interest. In the preceding 

 division of our subject, we have considered them as appli- 

 cable to various useful purposes, and expressed our regret, 

 at the same time, that no one qualified for the task had ever 

 bestowed on economical conchology an attentive examin- 

 ation. W T e cannot therefore consider the present condition 

 of the science as the result of the labours of its practical 

 admirers. The lovers of this study, as an agreeable amuse- 

 ment, have at all times been numerous, from the days of 



