1898.] NATURAL SCIENCES OF PHILADELPHIA. 421 



Sixteen other forms have a persistent range from the Miocene 

 through the Pliocene and Pleistocene periods down to the present 

 time. 



If we include these 16 as representatives of recent time, we have, 

 as noted above, 42 ; or, as pointed out by Dr. Dall in a letter from 

 which we quote, " nearly all the species as recent." 



One other form, Area lunula, is usually considered distinctively 

 Miocene, but its presence may be accounted for by considering it as 

 an introduction from the underlying Miocene beds, which are prob- 

 ably not over 50 feet from the surface in this region. Bearing upon 

 this, the writer may say that he has in his possession artesian well 

 borings recently made at Old Point Comfort and Norfolk, Va. At 

 Old Point Comfort, at the depth of 50 feet, were a number of shells, 

 among them such Miocene forms as Dosinia acetabulum and Pecten 

 madisonius, while at Norfolk there were obtained, at the depth of 

 105 feet, a fragment of Pecten madisonius, at 115 feet a perfect shell of 

 Gnathodon clathrodon, and at 175 feet a fragment of Pecten ehoreus. 



Respecting another form in the DismabSwamp bed, Arc. >lica- 

 tura, or perhaps a variety thereof, Dr. Dall says, after an ex ina- 

 tion by him of a number of specimens of this species which ~d 



sent him : "The Area you send is one which occurs in the ] 

 County Natural Well, North Carolina, and which was namK. j 

 Conrad Area lineolata ; but as there was already a species of this 

 name, D'Orbigny re-named it sublineolata. It appears to be a mu- 

 tation of J., plicatura, to which I have referred it in my (MS.) work 

 on the Tertiary Areas of the United States. There was one Plio- 

 cene species in the fossils from the Jericho Canal, 3 and as the Du- 

 plin beds are at the very top of the Miocene, it would not be strange 

 if A. sublineolata overlapped." 



Bearing still further upon the entire subject, we further quote Dr. 

 Dall from the same letter : — 



" The species from your list* are all recent except Area limula 

 [and Area sublineolata'], but some of them are not now found so far 

 north. Now we know that in Pliocene times some northward ad- 

 vance was made by the warm water species, such as Gnathodon and 

 Gyrena. There are too many recent species (assuming that the fauna 

 is not a mechanical mixture of shells of different ages) for the refer- 



3 This has reference to the bed near Suffolk, the forms from which appear 

 in the second of the preceding lists. 



4 Reference is here made only to the first list, that from near Wallaceton. 



