244 NEW FOSSIL SHELLS. 



N. CARINATA. PL. 34. FIG. 28. 



N. testa transversd, ovato-acuminatd, subinaqullaterali, antice rostratd, postice rotundatd, inflatd, crassiusculd, con- 

 centrice sulcatd ; sulcis parvis, crebris, regularibus. rotundatis; clivo umboniali elevato, carinato; margine basalt cur- 

 vato; margine dor sail media angulato, postice convexo, antice concavo; natibus minimc elevatis, recurvis; dentibus 

 angulalisj carinatis; anticis quatuordecim, posticis quindecim; cockled triangulari, profundd; margine interno 

 Integra. 



Shell transverse, ovate-acuminate, sub-inequilateral, anteriorly rostrate, posteriorly rounded, inflated, rather thick, 

 concentrically sulcate; sulci small, numerous, regular, rounded; umbonial slope elevated, carinate; basal margin 

 curved ; dorsal margin angular in the middle, .posteriorly convex, anteriorly concave: beaks very slightly elevated, 

 recurved ; teeth angular, carinate, fourteen anterior, fifteen posterior; fosset triangular, deep; internal margin crenu- 

 late. 



Diam. .15. Length .18. Breadth .11 of an inch. 



Remarks. The teeth are large and angular, with a carina on the outside edge of the 

 angle. The two series are nearly equal in number. 



This shell is very similar to the N. concentrica, Say: the points of difference are, 

 however, the greater proportionate length of our species, its carinate umbonial slope, 

 and peculiar teeth. It is also more equilateral, and has the series of teeth more nearly 

 equal. In these two last characters, it also approaches the N. media, Lea. 



N. ACUTIDENS, PL. 34. FIG. 29. 



N. testa tenui, Icevi, politd; dentibus magnis, longissimis, arcuatis, acutis, perpendicularibus ; cochlea minime pro- 

 fundd. 



Shell thin, smooth, polished; teeth large, very long, arcuate, acute, perpendicular; fosset shallow. 



Diam. Length Breadth of an inch. 



Remarks. I have but a fragment of the hinge of this shell, but the teeth are so re- 

 markable that they appear to distinguish it from all our other species. They are very 

 long, thin, pointed, and placed perpendicularly to the hinge margin, so as to project 

 beyond the shell and be seen nearly as well externally as internally. 



FAMILY MYTILUXE. 



GENUS MODIOLA. 

 M. SPINIGERA, PL. 35. FIG. 30. 



M . testa, quadrato-ellipticd, transversd, ineEquilaterali, postice truncatd, antice rotundatd, sub-inflatd, tenui, dia- 

 phand, striatd; striis parvis, concentricis, irregularibus ; clivo umboniali angulato; margine basali recto; margine 

 dorsali recto, spinoso; natibus prominentifrus, rotundatis. 



Shell quadrately-elliptical, transverse, inequilateral, posteriorly truncate, anteriorly rounded, somewhat inflated, 

 thin, diaphanous, striate; striae small, concentric, irregular; umbonial slope angulated; basal margin straight; dorsal 

 margin straight, spinous; beaks prominent, rounded. 



Diam .OS of an inch. Length .10. Breadth .14. 



Remarks. The spines on the dorsal margin are rather short and few in number ; they 

 project perpendicularly from the line of the margin. The substance of the shell is ex- 

 tremely thin. The beaks are long and somewhat incurved. 



