13 



GENERALIA 



Shelled mollusks belong to one of the most ancient groups of 

 animal life. Five hundred million years ago there lived in the Cam- 

 brian period of the earth's geologic history snails with shells so 

 complex and perfect that their presence can be explained only by 

 the existence of ancestral forms in a period far more distant. These 

 fossil remains are of great importance in the study and chronological 

 interpretation of the earth's geologic past. Their presence in strati- 

 fied rocks determines the periods in which successive layers of sedi- 

 ment were deposited in ancient seas, and the evolution of primitive 

 molluscan shells may be traced through these sedimentary deposits 

 to the shells of Recent families and genera. Certain shells from Ter- 

 tiary deposits in the Okeechobee and Caloosahatchee basins are of 

 types which persist in the living molluscan fauna of Florida waters. 



Emanuel Mendes da Costa/ 178 years ago wrote: — 



The study of Shells, or testaceous animals, is a branch of Natural 

 History, though not greatly useful in human oeconomy, yet perhaps, by 

 the infinite beauties of the subjects it treats of, is adapted to recreate 

 the senses, and insensibly to lead the amazed admirer into the contem- 

 plation of the glory of the Divinity, in their creation. 



The British conchologist George Perry, expressed a like feel- 

 ing in the introduction of his "Conchology, or the Natural History 

 of Shells", pubHshed at London in 1811. The sentiment was not 

 unique, for the symmetry and beauty of shells have suggested many 

 forms in art and architecture, and in some parts of the world their 

 use as objects of utility, ornament and symbolism is presently con- 

 tinuous with the practice of early man. North American Indian tribes 

 which practiced totemism used shells {Cypraea moneta) in their 

 ritual of death and resurrection, and so recently as eighteen forty- 

 eight to the eighties, Maplewood Institute for Young Ladies, at 

 Pittsfield, Massachusetts, listed Conchology in its regular curricu- 

 lum as a subject of cultural value to its students. 



Certain elementary principles must be understood before an 

 intelligent approach can be made to the study of shells. It is a 

 matter of common knowledge that animals differ widely in appear- 



1 Elements of Conchology, 1776 



