488 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. 51. 



that this upper zone should be regarded as the local equivalent of the 

 Orthaulax pugnax zone of Tampa, Florida. In this conclusion Dr. 

 T. W. Vaughan, in charge of the geological exploration of the coastal 

 plain, concurs. 



The lower zone has only 20 per cent of species common to the Or- 

 thaulax 'pugnax zone and Orthaulax is not among the fossils obtained 

 from it. Omitting the new forms, about one-fourth of the species 

 are common to the Vicksburgian Oligocene, and three-eighths are 

 also represented in the Jacksonian or Ooala horizons. Only about 

 6 per cent of the species of the lower zone are common to the marls of 

 the Chipola Kiver or the lower bed at Alum Bluff, while from the upper 

 zone about 10 per cent survive in the Chipola fauna. 



The lower zone, therefore, while distinctly younger than the Ocala 

 horizon, is believed by Doctor Vaughan and the writer to occupy a 

 position between that and the Orthaulax zone, near the base of the 

 upper Oligocene. 



Acknowledgments are due to the authorities of the United States 

 National Museum, in whose collection the types of this paper are 

 deposited, for facilities granted during its preparation. 



The plates have been prepared by the Division of Illustrations of 



the United States Geological Survey, and are used here by permission 



of the Director, who has authorized the publication of the present 



paper. 



DISTRIBUTION OF THE SPECIES. 



Upper 

 bed. 



Lower 

 bed. 



Vlcks- 

 burg. 



Orth- 

 aulax. 



Area subprotracta Heilprin . . 



cuculloides Conrad 



Glycymeris cookei Dall 



mississippiensis Conrad . . 

 Ostrea mauricensis Gabb 



vicksburgensis Conrad — 



cf . podagrina Dall 



Pecten alpha Dall 



suwanneesis Dall 



anatipes Morton 



Spondylus filiaris Dall 



Lima halensis Dall 



Modiolus grammatus Dall 



Gregariella, species 



Arcoperna infiata Dall 



Lithophaga nuda Dall 



Crassatelh'tcs paramcsus Dall. 

 Venericardia praecisa Dall . . . 



Cardita shepardi Dall 



Phacoides perovatus Dall 



wacissanus Dall 



species 



Miltha ocalana Dall 



hillsboro'ensis Heilprin . . . 

 Cardium glehosum Conrad . . . 



eversum Conrad 



species 



