64 Trans. Acad. Sci. of St. Louis. 



Anodonta opaca Lea. 



Trans. Am. Philos. Soc, 2d series, Vol. X, p. 285, PI. 



XXV, Fig. 46. Described from near New Orleans, and 



from near Little Rock, Arkansas. 

 This is a member of the grandis group and it is not sure 

 but that it should have been placed under the synonymy of 

 that species. It has not been seen by us in any collection from 

 Arkansas, and is admitted to this list on the strength of the 

 original description, which credits it to this State. 



There have been listed in the foregoing pages fifty-nine 

 species of Unionidoe, illustrating the three common North 

 American genera. Had there been recognized the great 

 number of synonymous forms, with which mere collectors seek 

 to enrich their cabinets, the list might have been greatly ex- 

 tended. At present we know, from Arkansas, 52 species of 

 Unio, 3 species of Margaritana, and 4 species of Anodonta. 



The Unionidoti abound in the streams of Arkansas ; varie- 

 ties or species may be relatively few, but individuals are very 

 abundant. They are to be sought in every conceivable con- 

 dition of bottom, and other factors of environment. Often 

 certain forms affect stated or well-known sorts of stations in 

 cold and clear, or warm and muddy waters ; others will be 

 found on gravelly or sandy bars, ordee ply buried in mud, close 

 to the river's margin. Careful search rarely fails to reveal 

 some form of interest. 



Louisville, Kentucky, Nov. 16, 1893. 



Issued January 3d, 1895. 



