OF THE UNITED STATES. 303 



Cabinet of the Academy and Philadelphia Mu- 

 seum. 



A beautiful little species, very remarkable by the 

 oblique course of the striae. It is rather common. 



4. T. *flexuosa. Shell suborbicular, white ; an- 

 terior margin longer than the posterior one, and less 

 obtusely rounded ; beak placed behind the middle, 

 not prominent ; surface obliquely sculptured with 

 very regular, parallel, impressed lines, which, on 

 the anterior margin, are four or five times refracted 

 and infracted alternately ; longitudinal striae none ; 

 transverse wrinkles minute. 



Length nine-twentieths of an inch. 



Breadth rather more. 



Thickness one-fourth of an inch. 



Inhabits the southern coast. 



Cabinet of the Academy and Philadelphia Mu- 

 seum. 



The fold on the anterior margin is very slight, but 

 perceptible, and is rendered remarkable by the zig- 

 zag course of the oblique striae over it. 



5. T. *tenera. Shell very thin arid fragile, 

 pellucid, compressed, transversely oblong- suboval, 

 whitish, iridescent, concentrically wrinkled ; basal 

 edge arquated, not rectilinear opposite to the beaks ; 

 hinge teeth two, larger one emarginate ; posterior 

 tooth but little elevated ; anterior tooth obsolete ; 

 heak placed behind the middle. 



Length three-tenths of an inch nearly. 



