FROM THE TERTIARY OF VIRGINIA. 237 



As but one valve of this shell, and that the left one, is before me, T cannot determine 

 the shape of the tooth. The pit to receive it is small and almost horizontal. 



This is, I believe, the only extinct species of Mya as yet found in our Tertiary. 



GENUS THRACIA, (LEACH.) 

 T. TRANSVERSA, PL. 34. FIG. 11. 



T. testa sub-ellipticd } valde incequilaterali, postice acuminato-rotundatd, antice truncatd, sub-compressd, tenui. 

 media Icevi, posticc et antice concentrice striatd; clivo umboniali rotundato; margine basali curvato; margine dorsali 

 media angulato } postice convexo. antice concavo; natibus sub-aculis; callo nymphali parvo, obliquo. 



Shell sub-elliptical, very inequilateral, acuminately rounded posteriorly, truncate anteriorly, sub-compressed, thin, 

 smooth centrally, striate posteriorly and anteriorly; umbonial slope rounded ; basal margin curved; dorsal margin 

 angular in the middle, posteriorly convex, anteriorly concave; beaks somewhat acute; nymphal callosity small, 

 oblique. 



Diam. .10. Length .18. Breadth .28 of an inch. 



Remarks. From the shape of the anterior margin, I conclude that the shell must have 

 gaped considerably there, but as I have no pair of valves, I cannot be certain. The sinus 

 of the palleal impression is deep, and near the anterior cicatrix. In this character, it 

 differs from the rest of the genus. 



This is, I believe, the first Thracia found in our Tertiary deposites. Deshayes, in his 

 tables, gives four as the number of European Tertiary species. The present one is the 

 smallest, of the genus. 



GENUS ANATINA. 

 A. TELLINOIDES, PL. 34. FIG. 12. 



A. testa ovato-triangulari, transversd, postice angulatd, antice rotundatd, compressd, postice undulatd, tenui, con- 

 centrice striatd; striis crebris minutis; margine basali sub-flexuoso; natibus compressis, prominentibus ; dentibus 

 lateralibus magnis; cochlea obliqud, ovato-acuminatd, minime profundd; cicatricibus magnis. 



Shell ovate-triangular, transverse, angular posteriorly, rounded anteriorly, compressed, posteriorly undulate, thin, 

 concentrically striate ; striae numerous, minute ; basal margin slightly flexuose ; beaks compressed, prominent : lateral 

 teeth large; fosset oblique, ovate-acuminate, shallow; cicatrices large. 



Diam. .25. Length .45. Breadth of an inch. 



Remarks. Of the lateral teeth, the posterior one is much the longer. The fosset is 

 small, quite oblique, acute above and rounded below. The broad undulation on the pos- 

 terior part of the shell gives it very much the appearance of a Tellina, when viewed 

 externally. The lines of growth are small, very numerous and irregular. 



This species is quite thin and fragile. Out of some half a dozen specimens, I have but 

 one perfect valve, and that is a very young one. I am therefore unable to give all the 

 dimensions. 



Judging from description, this shell is not unlike the A. antiqua, Conrad, but the dif- 

 ference in size and sculpture, and the posterior undulation distinguish them at once. 



VOL. ix. 63 



