OF NEW" TERTIARY FOSSILS. 123 



T. SERiCA. PI. 12, fig. 28. — Elliptical, inequivalved ; beaks nearest the posterior end ; concentric lines 

 very minute and closely arranged ; anterior side slightly bent or reflected. Length 7-10. 



T. vicKSBURGENSis. PI. 12, fig. 32. — Triangular, small, with regular minute concentric lines; anterior end 

 rounded ; posterior submargin angular or obscurely carinated, the end obliquely truncated ; posterior 

 side shortest, and slightly bent or waved ; lateral teeth in the right valve only. Length 3-10. Height i. 



T. PEROVATA. PI. 12, fig. 29. — Ovate, very thin, very inequilateral, compressed, smooth ; posterior side 

 subcuneiform, extremity acutely rounded ; lunule very narrow, elongated, lanceolate. 



DONAX. 



D. FUNERATA. PL 13, fig. 9. — Triangular, small, convex, with obsolete radiating lines ; anterior side short, 

 end truncated, direct; margin within finely crenulated; lateral teeth none. Length 3-10. 



Very rare. I found it about eight miles North East of Vicksburg. 



CYTHEREA. 



C. ASTARTiFORMis. PI. 1 3, fig. 13. — Trigonal, elevated, ventricose, subequilateral, with numerous regular 

 concentric grooves and obtuse ridges ; lunule not defined ; summits prominent ; umbo flattened. 

 Length 6-10. Height 4. 



This shell has a remarkable resemblance on the exterior to some species of 

 Astarte. Rare. 



C. iMiTABiLis. PI. 13, fig. 14. — Cordate, inequilateral, plano-convex, with numerous concentric prominent 

 acute ribs ; extremities rounded ; basal margin regularly curved ; lunule ovate, defined by an impressed 

 line. Length 1 7-10. Height 1 3-10. Common. 



C. MississippiENsis. PI. 13, fig. 16. — Subtriangular, ventricose, elevated, with prominent concentric acute 

 ribs, rather distant, and with irregular intervals and fine intermediate lines ; posterior margin 

 somewhat curved ; basal margin profoundly rounded ; summits prominent ; inner margin entire. 

 Length li. Height the same nearly. Rare. 



C. soBRiNA. PI. 13, fig. 17c — Subovate, ventricose, polished; with rather obtuse irregular, distant, 

 concentric, impressed lines ; umbo entire ; extremities rounded ; base regularly curved. Length 1 1-10. 

 Height 9-10. 



Very abundant. Almost always with disunited valves. It is quite thick on the 

 anterior side towards the summit. 



C. PERBREvis. PI. 13, fig. 18. — Ovate-triangular, elevated, ventricose ; the posterior and anterior margins 

 equally declining and very oblique, the anterior one straight, the posterior slightly curved ; beaks 

 medial ; surface with numerous regular impressed lines ; basal margin rounded. Length and 

 height 6-10. 



It is of the size, and has somewhat the form of V. astartiformis, but the greater 

 elevation, convex umbo, numerous impressed lines, and more rounded base, 

 distinguish it from that species. Rare. 



32 



