of the Yorktown and Duplin Formations. 309 



in the Duplin by five species, two of which are present in the 

 Alum Bluff formation of Florida, is unknown in the Yorktown. 

 Pymda and three species of Cypraeidae, all of them present in 

 the Bowden marls as well as in the Duplin and Waccamaw, 

 have no representatives north of Hatteras. Of the seven 

 Recent species of Muricidae represented in the Tertiary, the 

 only one present in the Yorktown is Eupleura eaudata Say, a 

 form which ranges in the Recent seas from Cape Cod to 

 Charlotte Harbor and the West Indies, while of the remaining 

 six Muricidae, half of them range from southern North 

 Carolina southward, while the other half have not been recorded 

 north of Florida. The group of Triforis nigrocincta and of 

 Cerithiopsis subidata exhibit in their Tertiary range from 

 Virginia to Florida the same line of variation as do the Recent 

 representatives. The distribution of the Tertiary Naticidae 

 is obviously governed by latitude. The two Recent species 

 which range from New England to the Gulf or the West 

 Indies, Natica pusilla Say and Polynices duplicatus (Say), 

 are present in both the Yorktown and the Duplin faunas. 

 Natica canrena Linne, which has been reported from Hatteras 

 to Carthagena, and is very abundant in the Bowden beds, is 

 unknown in the Yorktown, while Polynices heros (Say), which 

 ranges from Labrador to Hogg Island, Yirginia, is well 

 represented in Yirginia and northern North Carolina, but 

 exceedingly rare in the Duplin, and altogether absent in the 

 Waccamaw. 



The dissimilarity between the Duplin and Waccamaw 

 faunas is governed by time rather than place. Both contain a 

 larger percentage of Floridian species than does the Recent 

 North Carolina fauna, and while the danger of exaggerating 

 the importance of the occurrence of a single individual of a 

 characteristic Floridian species must be avoided, the occurrence 

 of thirty-six such species, against six in the Yorktown, cannot 

 but carry a considerable significance. The influence of ocean 

 currents on the distribution of marine life, which has been so 

 strongly emphasized by Dr. Bartsch in his study of the west 

 coast Pyramidellidse, and other groups of small univalves, 

 was doubtless potent in Tertiary times. Dr. Dall, in his dis- 

 cussion of Tertiary conditions along the east coast, suggested 

 the elimination of the cool inshore current, of the earlier 

 Miocene, and the reestablishment of a Tertiary Gulf Stream 

 as the probable cause of the sub-tropical aspect of the Duplin 

 fauna,* and later investigations have done much to substantiate 

 this theory. It seems probable, however, that this late 

 Miocene Gulf Stream hugged the North Carolina shore even 



*Dall, 1903, Trans. Wagner Free Inst. Sci., Philadelphia, vol. iii, pt. vi, 

 pp. 1598-1599. 



