On the Secondary and Tertiary Formations. 347 



L. radians. Orbicular, convex, with minutely waved or rugose con- 

 centric striae, and radiating strise obsolete on the middle of the valves, 

 and most distinct on the anterior side ; posterior submargin destitute of 

 radiating lines ; beaks central, prominent ; margin crenulated. This 

 species is recent at Mobile Point, Ala., and occurs near Newbern, N. C. 



Mytilus. 

 Myt.ilus incrassatus. Thick, much inflated ; anterior margin slightly- 

 incurved near the middle ; basal margin not obtusely rounded ; hinge 

 thick, with slightly prominent robust teeth. Length, about 3 inches. 



Caedium. 

 Cardlum sublineatum. Plate 11, fig. 13. Obliquely obovate, thin, 

 slightly ventricose, with obsolete radiating lines, most distinct near the 

 ends ; submargins of anterior and posterior sides destitute of radiating 

 lines ; within striated ; margin crenulated. 



Gnathodon. 

 Gnathodon minor. Plate II, fig. 14. Trigonal, convex-depressed, 

 posterior margin truncated and nearly direct. This makes the fourth 

 species of this interesting genus, two recent and two fossil. 



Amphidesma. 



Amphidesma constricta. Plate II, fig. 15. Oblong oval, ventricose ; 

 basal margin opposite the apex slightly contracted ; end margins round- 

 ed ; beaks nearest the posterior extremity ; fosset profound ; cardinal 

 teeth prominent, lateral teeth none. 



A. protexta. Oblongo-elliptical, compressed, with minute raised 

 punctse ; basal margin straight ; apex prominent, about one fourth the 

 length of the valve from the posterior extremity ; posterior side slightly 

 reflected ; lateral teeth none. Length, § inch. 



A. nuculoides. Ovate, convex, with very regular minute concentric 

 lines ; anterior extremity acutely rounded ; beaks near the posterior 

 extremity ; basal margin arcuate ; lateral teeth obsolete. 



Cardita. 



Cardita perplana. Plate II, fig. 16. Trigonal, nearly flat ; ribs 

 about eleven, angular, minutely granulated. 



C. ahbreviata. Plate II, fig. 17. Trigonal, elevated, convex-de- 

 pressed, ribs about eleven, convex, minutely granulated ; posterior ex- 

 tremity angulated. This and the preceding species belong to the genus 

 Venericardia of Lam, 



Natica. 



Natica Caroliniana. Plate II, fig. 18. Obliquely suboval, with ob- 

 solete spiral lines ; umbilicus large, with a central rounded prominent 

 thick carina ; apex prominent. 



