the same in mineral character, that, for instance near Claiborne, 

 where the shells are silicificd.. 



It has been remarked of the Eocene deposits of Europe, that they 

 fill depressions or basins in the chalk. The equivalent formation 

 in Alabama, fills valleys or depressions in a white argillaceous very 

 friable limestone, which Dr. Morton has shown to be cretaceous 

 and analogous to the Maestricht beds. This limestone, like the 

 chalk of England, forms a rolling or undulating country and appears 

 to have been subjected to extensive denudation. The upper bed of 

 the Eocene, in some places nearly fifty feet thick, has evidently 

 been formed of its detritus. 



Thefollnieiny tenn are adopted for tltt American Tertiary formation*. 



Ifyper Tertiary or Neieer Pliocene. Near Newbern, N. C. near the mouth 

 of the Potomac river, Md. Charleston, S. C. Nearly all the spe- 

 cies inhabit the coast of the United States. 



Medial Tertiary or Older Pliocene. St. Marys river, Md. parls of Lan- 

 caster county, Va. Yorktown. Va. James river near Srnithfield, Va. 

 Suffolk, Va.' Stow creek, Cumberland co. N. J. Charlotte Hall, 

 S. Marys co. Md. Choptunk river near Easton. Md. Of 150 sp- 

 cics, 40 inhabit the coast of the United States and several others 

 live in remote seas. 



Lmter Tertiary or Kdeene. Upper llarlborough, Md. Piscataway and 

 Fort Washington, Md. Vance's Ferry on Santee river, 8. C. 

 Orange-burgh, S. C. Shell Bluff, Ga. Wilcox co. Al. Claiborne, Al. 

 St. Stephens, Al. parts of West Florida, Natchex, Mi. near Mon- 

 roe! on Ouachita, L. No species inhabits the Atlantic coast, and 

 of 'two hundred species only two have been found in the Pliocene. 



It is necessary to observe, that all the species of Eocene fossils de- 

 scribed in the following pages, unless where credit is given or no refer- 

 ence made, were published before Mr. Lea's "Contributions to Geology". 

 No. 8 was published August, ia33, and No. 4, October, 1883. They 

 have been reprinted in order to group together the species of each genus. 



Corrigenda. 



Tab. 2, fig. 2. This was described as P. piilrinatu*. but it is now as- 

 certained to be very distinct, and it is proposed to name it P. lentifonui*. 

 Fig. 8 closely resembles P. raruibili*, of Sowerby ; but in comparing spe- 

 cimens of that species, given me by Richard C. Taylor, Esq., with the 

 American analogue, I find that in the latter the marginal teeth are wider, 

 fewer in number, and much more ornamental. 



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