OF NEW TERTIARY FOSSILS. 125 



PECTUNCULUS. 



P. ARCTATus. PI. 13, fig. 24i. — Short-ovate, convex-depressed, with little prominent flattened radii, 

 divided by a longitudinal impressed line towards the base; anterior margin truncated; posterior 

 margin nearly rectilinear. Length |. Height 6-10. 



Rare, and occurs on the bank of Yazoo river, about fourteen miles from Vicks- 

 burg. 



P. MississippiENSis. PI. 13, fig. 25. — Orbicular, ventricose ; length and height equal ; disk with slightly 

 prominent fine radii, minutely crenulated ; series of teeth uninterrupted ; inner margin finely 

 crenulated. 



NUCULA. 



N. SERicA. PI. 13, fig. 29. — Subelliptical, with minute regular concentric closely arranged lines; anterior 

 end acutely angular ; posterior end acutely rounded ; posterior side shortest. Length 4. Common. 



N. viCKSBURGENsis. PI. 13, fig. 26. — Obliquely subtriangular, convex, with minute obsolete radiating 

 lines about the base; lunule elliptical, very large and impressed. Length 5. Rare. 



KELLIA. 



K. OELONGA. PI, 1 3, fig. 28. — Oblong, convex, very thin, smooth, inequilateral ; anterior side longest ; 

 anterior extremity regularly rounded ; posterior extremity truncated ; base rounded. Length 3-10. 

 Rare. 



ARCA. 



A. MISSISSIPPIENSIS. PI. 13, figs. 11, 15. — A species of Area occurs in great abundance at Vicksburg, 



which Lesueur obtained many years since and named it, but I have forgotten the name, and know 

 not whether he published it in Europe or not. It is rhomboidal, ventricose, with rather distant ribs 

 in the right valve, slightly grooved in the middle ; in the left valve ribs double and granulated ; inner 

 margin profoundly toothed. Length 8-10. 



BYSSOARCA. 



B. LIMA. PI. 13, fig. 23. — Trapezoidal, cancellated and granulated ; radii largest on anterior and posterior 



slopes, but becoming obsolete towards the posterior extremity ; end angular, margin above obliquely 

 truncated ; anterior end widely truncated, nearly direct ; basal margin undulated, irregular and very 

 variable in outline ; hinge line crenulated under the beaks, profoundly toothed towards the 

 extremities; cardinal area with lines strongly defined and angulated under the apex. Length 2 9-10. 

 Rare. 



B. MISSISSIPPIENSIS. PI. 13, fig. 32. — Trapezoidal, with numerous closely-arranged radiating lines, 

 crenulated by fine concentric lines, the crenulation most distinct anteriorly, where the radii are 

 largest ; anterior end truncated or a little convex, direct ; posterior margin obliquely truncated above ; 

 basal margin widely and profoundly arched ; hinge line long, linear, minutely crenulated, expanded 

 towards the extremities, and with prominent teeth ; cardinal area with fine very closely-arranged 

 lines, angulated under the apex. Length 1 6-10. 



