INTRODUCTION. 19 
of the genera are unknown on our coast ; some are found 
only in a fossil state in Europe, and others are entirely new. 
fam not perfectly satisfied that a single species is strictly 
analogous tothose from the Eocene Period of Europe, but the 
number of turrited shells and similar genera prove it to be of 
the same epoch. The Venericardia planicosta (as Cardita 
planicosta) has been noticed by Mr Conrad as being of this 
locality. This is at least a variety, for it differs from those 
of the Eocene of the Paris basin in the number of its ribs, 
if not in some other characters. Three specimens from 
this formation, in my cabinet, contain individually thirty- 
one, thirty-four and thirty-six ribs, while of the first four- 
teen counted from Claiborne, three gave twenty-seven, 
four gave twenty-eight, two gave twenty-nine, and five 
gave thirty ribs. Mr Conrad describes his specimen (from 
Maryland) as having about twenty-two ribs. There are 
two other species from Claiborne, which resemble those of 
the Eocene of the Paris basin. One is a Fusus, very simi- 
lar to the F. longevus of Lamarck, but the specimen 
being imperfect, I cannot decide upon it with precision ;* 
the other is Acteont lineatus, (see description) which very 
closely resembles the Tornatella inflata (Ferussac).} 
The formation near Fort Washington, on the Potomac, 
below the city of Washington, may, I think, be referred 
to the same period as that at Claiborne. I owe to the 
kindness of Professor Vanuxem, specimens obtained there, 
many years since. Some of these shells have been 
since described by Mr Conrad, Cucullea§ gigantea, Tur- 
ritella Mortoni, &c. Future investigations may produce 
such results as will enable us to trace, with more exact- 
* I propose for it the provisionary name of Claibornensis. 
t Tornatella (Lamarck). 
t Description des Coquilles Fossiles des Environs de Paris, t. 2, pl. 
24, figs. 4 and 5. 
§ Two species only of this genus have been observed in the Tertiary 
of Europe. Both are in the Eocene of Paris. 
