NATURAL SCIENCES OP PHILADELPHIA. 559 



North America. The fact of the writer's being actively engaged in professional 

 duties at a Military Hospital while committing to paper the results of his in- 

 vestigations, will be a sufficient excuse for any evidences of hasty composition 

 which may be apparent. 



Catalogue of the MIOCENE SHELLS of the Atlantic Slope. 



BY T. A. CONRAD. 



In the Miocene or Upper Tertiary formation of the Atlantic Slope there 

 have been collected about five hundred and eighty species of shells, two 

 hundred and seventy-two of which are Conchifera and three hundred and nine 

 Gasteropoda. The most northern limit of this formation appears to be in Glou- 

 cester County, New Jersey, and it underlies the eastern portions of Delaware, 

 Maryland, Virginia, North and South Carolina. I have included in the Miocene 

 formation that portion of the South Carolina Tertiary referred to the Pliocene 

 period by Tuomey and Holmes, because I can discover no line of demarcation 

 by which these tertiary strata can be divided into two distinct groups. The 

 extinct species common to South Carolina and the more Northern Stafs are 

 numerous, and the fauna can only be regarded as that of one geological era. 

 Some few of the species described by Tuomey and Holmes from the South 

 Carolina Tertiary occur also in New Jersey, at the most northern boundary of 

 the Miocene. The per eentage of recent species in South Carolina, it appears 

 to me, should be greatly reduced, and I would reject from the list as many as 

 eighteen, consisting of the following shells: Busycon canaliculatum, B. per- 

 versum, Strephona literata, Littorina irrorata, Natica canrena, Dolium galea, 

 Fasciolaria gigantea, F. distans, Pholas costata, P. oblongata, Petricola pfao- 

 ladiformis, Solen ensis, Lucina divaricata, L. Pennsylvania, Cardium magnum. 

 Mactra similis, Yoldia limatula, Strigilla fluxuosa. It may be that all the 

 species are extinct, but I have not had an opportunity of comparing all those 

 doubtful shells with the recent forms. Natica heros and N. duplicata, Say, 

 have fossil analogues in Maryland so closely resembling them that I find no 

 essential difference ; but the shells of this doubtful character are not more 

 than thirty in number out of five hundred and eighty-one species. Near the 

 coast, a Post-Pliocene or Pleistocene formation rests immediately on the Mio- 

 cene, replete with existing forms, but as a group resembling that of more 

 Southern latitudes on the coast of the United States. There is no inter- 

 mingling of extinct species between these two formations, and the passage is 

 almost as abrupt as between the Eocene and Miocene. 



The final subsidence of the Eocene appears to have been accompanied cy 

 Sttch an alteration of climate or other conditions as to have given origin to a 

 totally distinct terrestrial and marine fauna, the latter existing on an Eocene 

 and Cretaceous bed, extending from New Jersey to South Carolina inclusive, 

 and which appears to have been generally extinct and above the sea during ;b*> 

 existence of the European Pliocene faunas. 



Works referred to. 



C. Miocene Foss. Conrad, Medial Tertiary or Miocene Fossils of the U. S. 



C. Foss. Shells of Tert. Form. Conrad, Fossil Shells of the Tertiary Fcnsa- 

 tions of the United States. 1832. 



Trans. Amer. Philos. Soc. Transactions of the American Philosophical So- 

 ciety of Philadelphia, vol. ix. n. s. 1845; vol. vi. n. s. 1839. 



Sttlim. Jourr.. American Journal of Science and Arts. 



Journ. A. N. S. Journal of the Academy of Natural Sciences of Phila- 

 delphia. 



Procctd. A. N. S. Proceedings ditto. 



18U2.] 



