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fore, agreeably to any rules of modern nomenclature, the name 

 purpuretis seems fated to withstand all attacks, unless, indeed, it 

 can be proved, from Mr. Dillwyn's description itself, tliat be meant 

 this shell, when he described his contplanatus, and not that of the 

 figure to which he refers. 



Alasmodonta sculptilis. — Shell transversely suboval, with 

 green radiations : umbo and summit with six or seven rather sharp 

 undulations, which are transverse, rectilinear, at the extremities 

 abruptly arquated or reflected : dorsal and anterior margin from 

 the summits with numerous, slender, slightly elevated lines bend- 

 ing in different directions. 



This is evidently a young shell, but we know nothing of the 

 adult. The teeth are more like those of tlje undulata, nob., than 

 any other species, but the form and sculptured anterior margin 

 amply distinguish it. 



It was brought from Virginia by Mr. I. Lukens, and by him 

 presented to me. 



Alasmodonta edentula. — Shell transversely oblong-oval, 

 somewhat compressed, dark olivaceous or brownish, obsoletely 

 radiated (in the young :) nates behind the middle, but remote from 

 the posterior edge, but little prominent, undulated : anterior mar- 

 gin not remarkably compressed, and not radiated : within white, 

 margined with opake white more or less distinct, but sometimes 

 obsolete : teeth obsolete, but the peculiar curvature beneath the 

 beaks shows their locality. 



Length, one inch and seven-tenths ; breadth, three inches. Con- 

 vexity, one inch. Inhabits Wabash river. 



Approaches nearest to A. marginata, nob. ; but the want of 

 teeth, and the simple anterior margin, at once distinguish it. 



Cyclas edentula. — Shell transversely oval, inaequilateral, 

 with somewhat elevated and regular transverse lines : beak not ele- 

 vated above the general surface ; cardinal tooth very small, lineolar, 

 oblique and not elevated higher than the edge of the hinge mar- 

 gin : color brown : umbones decorticated. 



Length, seven-twentieths of an inch. Breadth, two-fifths of an 

 inch. Inhabits Canandaigua Lake. 



This is distinguishable by the diminutive teeth, which are not 

 visible in a profile view of the hinge. 



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