No. XIII. 



Description of a New Genus of the Family of Naiades, inclu' 

 ding Eight Species, Four of which are New ; also the De- 

 scription of Eleven New Species of the Genus Unio from 

 the Rivers of the United States : ivith Observations on some 

 of the Characters of the Naiades. By Isaac Lea, M.A.P.S. 

 M.A.N.S.P., Sfc. Bead March 6th, 1829. 



T HAD the pleasure to present to this Society in November, 

 -■-1827, a description of six new species of [the genus Unio, 

 which they did me the honour to publish. Since that period 

 I have continued to collect and examine the genera of the 

 family of Naiades with great interest, and more success than 

 I could have anticipated. I propose in this paper to describe 

 fifteen new species, a number which rarely falls to the lot of 

 a naturalist at one period ; and I shall previously indulge my- 

 self in some observations respecting their characters, ha- 

 bits, &c. 



Strong objections have been made to the study of concho- 

 logy by persons unacquainted with this branch of zoology, 

 and it has been alleged that a collection of shells is merely 

 a collection of the houses or habitations of an animal carefully 

 removed by the naturalist or destroyed by other causes, and 

 therefore unworthy the time and attention of the student of 

 nature. This assertion betrays ignorance, and recoils on the 

 observer ; for it niay with truth be said, that no part of the 



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