Mr. Barnes on the Genera Unio and Alasmodonta. 107 
CONCHOLOGY: 
Arr. VI.—On the Genera Unio and Alasmodonta; with 
Introductory Remarks: by D. W. Barnes, M. A. Mem- 
ber of the New-York Lyceum of Natural History. 
- [Read before the Lyceum.] 
INTRODUCTORY REMARKS. 
Tue family of the Natades, according to M. Lamarck, 
contains four genera of fresh water Bivales, viz. Sem, Hy- 
ria, Anodonta and Iridina. To this family belong the 
sas of Dr. Leach, and the Alasmodonta of Mr. Say. Sev- 
eral undescribed 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. 
he 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 ef 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 MM. 
Lamarck, and adopted by M. de air and has thus ta- 
ken its place i 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 epg ti 
brought from the N. W. Territory, was unknown to 
For our first view of them we were indebted to the zeal ol 
