OF NEW TERTIARY FOSSILS. 121 



T. TEREXiLis. PI. 13, fig. 2. — Narrow-fusiform, with convex volutions, having large, rounded, longitudinal 

 ribs, about six on the large whorl ; revolving lines strong, prominent, distant, with a fine intermediate 

 line ; longitudinal wrinkles minute and ornamental ; aperture narrow ; labrum striated within ; 

 columella with two large plaits; beak long and narrow. Length 1. 



Distinguished from the preceding by its narrower outline, fewer and larger plaits 

 on the pillar, &c. It is probably a much smaller species, but as I have one specimen 

 only, its greatest size cannot be determined. 



PANOPiEA. 



P. OBLONGATA. PI. 1 3, fig. 12. — Elongated, Very inequilateral, ventricose ; extremities rounded ; umbo 

 prominent, undulated; valves slightly contracted at base in a line with the umbones; valves gaping 

 at both ends. Length 33. 



Occurs in its original vertical position, generally with connected valves, but it is 

 extremely friable and difficult to obtain. 



MACTRA. 



M. MississiPPiENSis. PI. 12, fig. 14. — Subtriangular, equilateral, very tliin and fragile, plano-convex ; 

 dorsal margin very oblique, nearly straight, extremity acutely rounded, much above the line of the 

 base, which is regularly curved ; summit prominent ; lunule elongated, defined by an impressed line ; 

 umbonial slope nearly terminal, angulated and carinated by a thin line. Length 1 8-10. Height 1 4-10. 



Proportionally more elevated than M. prceteiiuis, of Claiborne, Alabama, and a 

 much larger species. Rare. 



M. FUNERATA. PL 12, fig. 13. — Triangular, small, convex; much longer than high, equilateral; posterior 

 end angular. Length 3-10. Rare. 



AMPHIDESMA. 



A. MISSISSIPPIENSIS. PI. 12, fig. 20. — Oblong-oval, somewhat compressed, inequilateral, smooth, with a few 

 distant concentric impressed lines , posterior side with a slight fold, end obtusely rounded ; anterior end 

 rounded ; cartilage pit very narrow, elliptical ; lateral teeth in the right valve distinct, in the left 

 wanting? Length 1 1-10. Height 7-10. 



A. PEROVATA. PI. 12, fig. 21. — Ovate, inequilateral, plano-convex, smooth ; anterior end sub-truncated; 

 ligament margin oblique, curving regularly towards the extremity, which is acutely rounded ; basal 

 margin rounded ; lateral teeth in the left valve ; right valve unknown, 



PSAMMOBIA. 



P. PAPYRiA. PI. 12, figs. 15, 17. — Oblong-oval, or somewhat rhomboidal; very thin, compressed; 

 posterior side rather wider than anterior ; and posterior to the umbonial slope, which is undefined, 

 there are concentric lamelloeform lines ; anterior margin obliquely rounded ; dorsal margin parallel 

 with the base. Length 11. Rare, 



