SHELLS AND MOLLUSCOUS ANIMALS. 211 



like the lungs of other animals destined to inhale 

 atmospheric air ; but the Gasteropoda, formed to 

 inhabit the sea, have gills or branchiae placed on 

 different parts of their bodies. The structure of 

 some of these gills is exquisitely beautiful. In some 

 they form a number of rays, like a lovely flower, 

 on the back of the animal : in others they are like 

 long rows of leaflets : while in many they are 

 shaped like the teeth of a comb, thus forming 

 good characters for a scientific classification. 



Every one is familiar with some of the common 

 shells of the animals of this class. Our beaches 

 are strewed with them, they lie among our rocks, 

 and some are found on our sandy shores. Many 

 little shells of great beauty lurk in the heaps of 

 drifted sand, or hang about the roots of sea-weeds, 

 needing a microscope for their examination. Not 

 a lake, or pond, or ditch but has its own tribes 

 lying among the mud at its base, or hiding among 

 the plants which surround it, or forming a carpet on 

 its surface. Land shells, too, of this order exist 

 everywhere ; and the bitten leaves of our choicest 

 garden flowers, too often leave the silvery traces 

 of the snail or slug, which has remorselessly made 

 its meal upon them during the rainy day or the 

 moist evening. The sea itself has its myriads of 

 these animals, and a greater number of genera 

 and species belong to this class than to the 

 Conchifera. 



All who have wandered among the rocks on 

 our shores, know that univalve so frequent upon 

 them, the common Limpet (Patella vulgata], which 

 adheres as firmly to the rock as if it were a portion 

 of it, while its empty shells, like so many little 

 cups, lie strewed around. It is often completely 

 p 2 



