170 



ones ; compound ligament exterior ; palleal line entire, uniting the 

 two muscular impressions. 



Ohs. I formed this genus to receive several species of fluviatile 

 bivalves, which the characters of Unio and Anodonta exclude. 

 Lamarck placed some of the species in his genus Vnio, notwith- 

 standing his character of lateral teeth, " allongee, comprimee, 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 Regno Animal unites all the 

 genera of this family in Anodonta and Vnio ; 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 

 Alasmisodonta, 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 Unio, 

 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 

 by 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. 



