MARINE MOLLUSCA OF THE UNITED STATES. 149 



4. T. TENTA, Say. Figs. 350, 351. 



American Conchology, PI. 65, f. 3. 



Shell small, oval, white ; shortest behind, narrowed, much de : 

 fleeted and widely gaping ; lines of growth very fine. Two cardi- 

 nal teeth in the right and one in the left valve ; a posterior lateral 

 tooth in the right valve and a corresponding groove in the left. 

 Length 15, height 10 mill. 



Massachusetts to So. Carolina. 



This species is generally larger than T. tenera, and has not its 

 polished surface. It differs from others principally in being less 

 triangular, more strongly deflected, and in its widely gaping pos- 

 terior portion. 



5. T. MODESTA, Verrill. tfigs. 352, 353. 



(Angulus.) Am. Journ. Sci., 285, t. 6, f. 2, 2a. 1872. 

 Shell smooth, shining, more or less iridescent, with very fine 

 concentric striae. Form similar to T. tenera, but more oblong 

 and with the anterior dorsal margin nearly straight or even 

 slightly concave ; beaks at about the posterior third and scarcely 

 prominent ; the posterior end slopes rapidly and is subtruncate 

 at the end ; the ventral margin is but slightly convex in the 

 middle, and subparallel with the dorsal margin. Teeth and 

 hinge margin stronger than in tenera. Color pink, light straw- 

 color or white ; often banded concentrically with these colors. 



New England. 



6. T. IRIS, Say. Fig. 354. 



Journ. Philad. Acad., ii. 302. 1822. 



Shell very thin and fragile, pellucid, compressed, transversely 

 oblong, suboval ; minute concentric wrinkles, crossed by oblique 

 striae which do not attain the margin ; margin narrowed and sub- 

 acute ; basal edge straight, opposite the beaks. Color, white, 

 iridescent, with a rosaceous disk and one or two anterior rays. 



Length 12.5, height 7.5 mill. 



North Carolina, southwards. 



7. T. BREVIFRONS, Say. Figs. 355-351. 



Am. Conchology, t. 64, f. 1. 



Shell oval, thin, and fragile, not very convex, white, tinged 

 with pale dull fulvous ; with transverse slender striae and obsolete 

 radiating ones ; deeper colored within ; cardinal teeth two in the 

 left valve and one in the right valve ; lateral teeth none. 



South Carolina. 



