340 



TRANSACTIONS OF THEJ 



produced, surface with distinct concentric irregular un- 

 dulations ; beaks distant from the anterior margin. 



Occurs abundantly at Piscataway, Maryland, generally 

 in casts in the indurated marl. Distorted casts of a 

 Panopea, probably the same species, are common near 

 Orangeburg, South Carolina. 



Modiola crelacea. PI. 13, Jig. 2. Shell inflated, 

 narrowed inferiorly; umbonial slope angulated. 



This species is remarkable for its inflated form, which 

 gives it a rounded contour. It is a cast from the upper 

 division of the cretaceous series of Clark county, Ala- 

 bama, whence it was received by Dr Harlan, to whom I 

 am indebted for the opportunity to describe and figure it. 



Turritella Immerosa. FL 13, fig. 3. Shell turrited, 

 subulate ; whorls with fine regular revolving striae, an 

 obtuse slight elevation on the summit, and a shallow 

 groove at base of each. 



From the eocene at Piscataway, Maryland. 



ZOOPHYTA. 



Lithodendi'on lineatus. PL 13, fig. 4. Gampanu- 

 late ; laminse of the rays finely crenulated ; surface longi- 

 tudinally and delicately striated. 



A beautiful species, not uncommon in the pliocene 

 beds of Virginia, attached to various shells. 



I have rather too hastily supposed that the equivalent 

 of Mr LyelPs miocene period occurred in this country; 

 but I am now convinced that all above the eocene may 

 more properly be termed older and newer pliocene. 

 There is no gradual transition from the older to the 

 newer tertiary, but so vast has been the change, or the 

 period of time which elapsed between them, that a single 

 species of testacea has alone survived it; besides, so many 

 recent species of the Atlantic coast of North America 

 occur in every deposit of the tertiary above the eocene, 



