68 INTRODUCTION TO CONCHOLOGY. 



to the surface of the water, and thus exposes the ova to the 

 full influence of solar light and heat. 



The science of Conchology continually presents fresh sub- 

 jects of interest to its votaries ; and as regards the general 

 habits of the Gastropods, many interesting phenomena have 

 become developed. The greater number attach themselves to 

 marine rocks, or masses of stone ; they also creep into cavities 

 and crevices, and hide in tufts of coral, or among sand and 

 mud. The Maphis even fixes his stationary abode in a growing 

 mass of white coral ; but then, in order to maintain a neces- 

 sary communication with the surrounding element, he alters 

 his spiral mode of growth in accordance with the increase 

 of the coral, and pursues a nearly straight course, in order 

 to keep pace with the advancing surface of his rocky bed. 

 The lanthina, or Sea-snail, and the Stylifer, are equally 

 deserving of brief notice : the first, a creature that floats on 

 the bosom of the ocean by means of numerous air-bladders 

 affixed to the foot ; the second, of parasitic habits, living 

 imbedded in the soft parts of the Star-fish. 



Shells belonging to the class of Gastropods are either of a 

 spiral or conical structure. Among these the first are most 

 numerous, though without including any specimens of equal 

 weight and dimensions with the Giant Clam of Bivalves. 



