170 
ones ; compound ligament exterior ; palleal line entire, uniting tke 
two muscular impressions. 
Ohs. I formed this genus to receive several species of fluviatile 
bivalves, which the characters of Unto and Anodonta exclude. 
Lamarck placed some of the species in his genus JJnio, notwith- 
standing his character of lateral teeth, allongee, comprimSe, se 
prolongeant sous le corselet.^^ 
Blainville, in his Manuel,’' has placed the genus as a subgenus 
under Anodonta.^ with Iridina of Lamarck and Dipsas of Leach. 
Cuvier in the first edition of his Begne Animal unites all the 
genera of this family in Anodonta and Unio ; and is still followed 
in this arrrangement by some other naturalists, upon the principle 
that inosculating species destroy genera. They appear to forget 
that the same principle would reduce those two genera to a unit, 
and would in fact eliminate a great portion of those groups, in all 
departments of natural science. 
Four different names have been applied by as many writers, to 
designate this genus. Leach called it Damaris ; another name, 
according to Swainson, was given by Dr. Turton ; and a third, that 
of Margaritariaf^ by Mr. Schumacher. To all these generic names 
the A. margaritifera of Linne was referred by their respective 
authors, who do not appear to have been acquainted with either of 
the several species which inhabit our waters. 
Those who change the orthography of Anodonta to Anodon^ 
will write the name of this genus Alasmodon for the same reason. 
One author writes it Alasmidonta and Blainville changes it to 
Alasmisodontay without abbreviation. 
But those who assume the task of rejecting genera in this family, 
in order to be consistent, must revert to the principles laid down 
by Ferussac in his Essai d’une methode Conchyliologique,” pub- 
lished in 1807. He reduces all the Naiads to the genus Unioj 
and the remaining parts of his system, chiefly correspond with this 
view of the subject. Mr. Sowerby, in the Zool. Journal, 1824, has 
made the same proposition, though in his Grenera ” he retains 
* Essai d’un nouveaux systeme des habitations des Vers Testacees, 
1817. The priority of this date would lead me to adopt the name given 
hy that author, did it not appear that the work was not published for 
several years after it was printed. It was not known to the naturalists 
of this country, France, Germany or England until the year 1822. 
