ITNIO. 



GENERIC CIIARACTEll. 



vSliell unattached, generally transverse, equivalved, ine- 

 ([uilateral ; cardinal teeth one in each valve, irregular, ge- 

 nerally striated, simple or biparted ; an elongated lamelli- 

 form tooth on the anterior hinge margin of the left valve, 

 and two similar teeth on the corresponding margin of the 

 right valve ; muscular impressions two principal ones ; li- 

 gament exterior. 



OBSERVATIONS. 



In North America the shells of this genus excel those 

 of any other country in magnitude, beauty and diversity 

 of species. They are altogether inhabitants of fresh wa- 

 ter, and we have hardly a rivulet in the Union, in which 

 they are not to be found. Many of them are of a beau- 

 tiful perlaceous colour and consistence, and we are inform- 

 ed that some of the very thick ones of the Ohio, have !)een. 

 at Pittsburgh, successfully turnetl into buttons and orna- 

 ments. 



This genus is closely allied to Dipsas, Leach. Hvria 

 and luiDiNA, Lam.^ Alasmodonta, Nob.^ and Anodon- 

 TA, Brug. But the former has lamelliform teeth only ; 

 Hyria has lamelliform teeth on both sides ; Iridena and 

 Anouonta are destitute of teeth and Alasmodonta is 

 destitute of lamelliform teeth. To this exposition we may 

 add, as more remotely allied, the Megaues.ma of Uowd., 

 which has two cardinal teeth ou ouc valve iuid thi'ee iu 



PLATE IV. v. VI. 



