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. 

 I am not perfectly satisfied that a single species is strictly 

 analogous to those 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 Cardila 

 planicosta) has been noticed by Mr Conrad as being of this 

 locality. This is at least a variet}^ 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. long&vus of Lamarck, but the specimen 

 being imperfect, I cannot decide upon it with precision ;* 

 the other is Jlcteon^ lineatus, (see description) which very 

 closely resembles the Tornatella inflata (Ferussac)4 



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, Cucullcea 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). 



J Description des Coquilles Fossiles des Environs de Paris, t. 2, pi. 

 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. 



