Mr, Barnes on the Genera Unio and Masmodonta. 107 

 CONCHOLOGY, 



Art. VI. — On the Genera Unio and Alasmodonta ; with 

 Introductory Remarks : by D. W. Barnes, M. A. Mem- 

 her of the New- York Lyceum of Natural History. 



[Read before the Lyceum.] 



INTRODUCTORY REMARKS. 



The family of the Naiades, according to M, Lamarck^ 

 contains four genera of fresh water Bivales, viz. Unio, Hy- 

 ria, Anodonta and Iridina. To this family belong the Dip' 

 sas of Dr. Leach, and the Alasmodonta of Mr. Say. Sev- 

 eral andescribed species of the Genera Unio and AlasmO' 

 donta, were brought to our knowledge by the expedition 

 sent by our government in the summer of 1820, under Gov, 

 Cass, to explore the North Western Territory; and others 

 have since been obtained from various sources. 



Little has hitherto been done by our countrymen in de- 

 scribing these interesting productions of our lakes and rivers. 

 The only American work, of the kind, at present known, is 

 that of Mr. Thomas Say, who published at Philadelphia in 

 in the year 1819, " A description of the land and fresh-wa- 

 ter shells of the United States." This treatise had been pre- 

 viously published in Nicholson^s Encyclopedia. It deserves 

 the thanks, and ought to be in the possession of every Amer- 

 ican lover of Natural Science. It has been quoted by M, 

 Lamarck, and adopted by M. de Ferrusac, and has thus ta- 

 ken its place in the scientific world. 



But Mr. Say^s tract, though a very commendable perform- 

 ance, was necessarily imperfect. The author himself has 

 described thirty new species of univalves since the publica- 

 tion of his book, and a great part of the splendid collection, 

 brought from the N. W. Territory, was unknown to him. 

 For our first view of them we were indebted to the zeal and 



