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ARTICLE II. 



Observations on the Naiades ; and Descriptions of New Species of that, 

 and other Families. By Isaac Lea. Read hefore the American 

 Philosophical Society March 16, 1832. 



PRELIMINARY REMARKS. 



In presenting myself again before the Society with a new memoir in 

 that department of conchology which has so much engaged my atten- 

 tion for some years, an apology would seem almost necessary. My 

 zeal and love for the science generally will, I trust, be sufficient for 

 my present intrusion on its time. 



The family Naiades seems to have excited very little interest with 

 the older writers on natural history, and not much more among mo- 

 dern zoologists until within the present century. 



The progress of general knowledge, and the improvements in the 

 mechanic arts, have recently been greatly accelerated, and the disco- 

 veries and improvements in the study of natural science, have gone on 

 " pari passu" with them ; and we have every reason to believe that the 

 momentum which they have acquired will not be diminished, for, to 

 use the words of one of the most successful writers of the present day, 

 " there is growing up an enlightened public opinion" which no power 

 is likely to arrest, and which must carry us far towards a perfect state 

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