But it is not alone the beauty of 

 shells that renders them interesting. 

 Conchology, which treats of shells, 

 is as a science at least as old as 

 the days of Aristotle, the study of 

 which was resumed, along with that 

 of the other sciences, when the 

 dark ages had passed away. Since 

 the beginning of the nineteenth cen- 

 tury it has given place to a more ex- 

 tended and comprehensive study of 

 molluscous animals, the presence or 

 absence of a shell having been found 

 not to constitute one of the most im- 

 portant characteristics which distin- 

 guish different classes of mollusks. 

 Conchology was only the form of the 

 science suited to a time when the shell 

 was more considered than its inhabi- 

 tant. Yet it is claim.ed that the rela- 

 tions between shells and the mollusks 

 which possess them are such that the 

 labors of the merest conchologists have 

 contributed to the real advancement 

 of science, both zoological and geo- 

 logical. 



Shells consist of carbonate of lime 

 secreted by the animal and intermixed 

 with some animal matter. In the spe- 

 cies in which it is least developed it 

 appears as a hollow plate, which serves 

 as a protection to the breathing organ 

 and heart. The protuberances and 

 ridges seen on many univalve and 

 bivalve shells appear in the course of 

 their growth by the margin of the man- 

 tle, turning out at a considerable angle 

 and thus building up a plate in this po- 

 sition for a certain distance. This 

 growth then ceases, the mantle retracts, 

 or may be regarded as changing itself 

 into the shelly layers, and thus it ex- 

 tends in the original direction, carrying 

 out the shell with it, till it turns again 

 to form a second plate or ridge; and 

 so the process goes on. Many mol- 

 lusks possess the power of altering and 

 enlarging their shells to adapt them to 

 their growth, which they appear to do 

 as if by an intelligent will. 



The distinguishing marks of shells 

 are the number of parts of which they 

 are composed, and their peculiar forms 

 and prominences. Some consist of a 

 single piece, some of two pieces, and 

 some of three. The textures of shells 

 are described as pearl, fibrous, horny. 



and some are glassy and translucent. 

 The pearly shells are in alternate lay- 

 ers of very thin albuminous membrane 

 and carbonate of lime, which by their 

 minute undulations give the pearly 

 lustre. This structure is the least per- 

 manent and in some geological forma- 

 tions the shells that were provided 

 with it have disappeared, leaving only 

 their casts, while those of fibrous text- 

 ure are preserved unchanged. Colors, 

 however beautifully exhibited upon the 

 surface of shells, are to them no more 

 distinctive features than to the miner- 

 als and flowers upon which they are 

 also prominently displayed. They are 

 most richly developed upon those sur- 

 faces most exposed to the light and in 

 the class of shells found in shallow 

 waters. 



The whole number of species of mol- 

 luscous animals known is estimated at 

 about twelve thousand recent and fif- 

 teen thousand fossil. Many of the liv- 

 ing species furnish wholesome food, 

 and some are esteemed as delicacies. 

 The marine shells, by the immense 

 numbers in which they are produced, 

 perform an important office in abstract- 

 ing from the sea-water its excess of cal- 

 careous matter and thus aid in main- 

 taining its purit)'. 



As objects of beaut)-, shells have al- 

 ways been admired and frequently been 

 used as ornaments Some varieties 

 were used by the Athenians as ballots, 

 with the name upon them of the per- 

 son to be banished, whence the term 

 ostracism. Some shells have served 

 the purpose of coin among rude na- 

 tions. Others are noted for the pearls 

 which are secreted between their 

 valves around some foreign substances. 

 Mother-of-pearl is the polished shell of 

 nacreous. Rare species of shells are 

 highly prized by collectors, and single 

 specimens have been sold for large 

 sums. The South Sea Islanders use 

 the conch as an instrument of music, 

 blowing into the shell through the 

 broken top, thereby producing a loud 

 and mellow sound. It is a species of 

 sea conch which is represented by the 

 god Triton. In many rural parts of 

 the United States conchs are used in 

 place of dinner bells or tin horns to 

 call persons from a distance. 



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