4 



POPULAR CONCHOLOGY. 



an organ of motion, has been called the foot (c), is much 

 more universally found amongst mollusca than the head, 

 and is a member of considerable importance. It is very 

 muscular and flexible ; large and strong in Gasteropoda and 

 in the burrowing kinds of Conchifera, and rough in those 

 which bore into rocks, but scarcely existing in those at- 

 tached to other substances. A few words only in this 

 part of the work are necessary with regard to the internal 

 construction of these animals. They possess the usual 

 organs necessary for the support of life, a nervous system, 

 a heart, with its attendant veins and arteries, furnished 

 with a cold and white or bluish blood, and an apparatus 

 for breathing, consisting, in those which live in water, of 

 branchiae placed externally or internally, and so arranged as 

 to have a stream of water continually presented to them, 

 and in those which live in air, of organs fit for its res- 

 piration. 



Mollusca are to be found in all parts of the world, in 

 the sea, in rivers, and on land, and dhTer in their con- 

 struction and habits according to their locality. A great 

 number have their residence in the sea, and are unable to 

 exist out of salt water : of these some continue near the 

 surface, others have the power of moving through the deep 

 waters, and others again are attached by various means 

 to rocks and corals. Many species are met with, living 

 on the shore, in the sand, mud, or clhTs, and many in 

 rivers : the land also has its peculiar varieties, where they 

 live under ground, in holes of trees, or in moist and 

 marshy places. These different habitations give a general 

 name to the Mollusca which are found in them, as Pela- 

 gic*, to those which reside in the deep recesses of the 

 ocean, Litoral], to such as are found on the coast, Flu- 



* From pelagus, Lat., the deep sea. 

 | From litus, Lat., the sea shore. 



