1554 



collections are needed before the precise distribution of these species in time 

 can be known. There is some question in my own mind as to whether the 

 Jacksonian Orbitoides, noted for its larger size and referred to by Colonel 

 Casey, is not the O. papyraceus instead of the O. Mantelli, but these questions 

 must be solved by an expert in foraminifera. 



Colonel Casey recognizes two distinct horizons in the Vicksburg bluff, re- 

 garding the two lower strata of O. Meyer as a single faunal group differing 

 from the clayey upper marls by about fifty per cent, of its included species. 

 If this is confirmed by more extended researches, the upper bed should receive 

 a distinctive name. It is in this bed and not the limestone that Orbitoides \s 

 a characteristic fossil. Colonel Casey also notes in regard to the fossils of 

 Byram Station on the Pearl River that they appear intermediate between the 

 Vicksburgian and Red Bluff, many of the species belonging to the former 

 fauna, while the Byram deposit also contains a considerable number which are 

 peculiar to itself. Doubtless the thorough exploration of these different beds 

 will greatly enlarge the number of recognizable faunas and clear up much that 

 is doubtful at present in regard to the progressive evolution of the inverte- 

 brates of our Tertiary. 



From the observations on the typical Vicksburgian by Colonel Casey it 

 seems probable that the Orbitoidal limestone which forms the mass of the 

 Floridian plateau, and which has been, in this work and in the literature, gen- 

 erally called the Vicksburg limestone, may really form a different horizon 

 altogether from the typical Vicksburgian and be intermediate between the 

 latter and the nummulitic Ocala limestone. In order to promote clearness 

 and avoid confusion it is probably advisable to adopt a distinct name for the 

 Orbitoidal phase or formation, for which I would suggest the term Peninsular 

 limestone. This is intended, not as a permanent formation-name, but as a 

 general term for the fundamental plateau limestone of Florida, in which a close 

 and thorough study in the future may result in the discrimination of more than 

 one horizon or zone. 



For the statistics used in the general table I have been obliged to take 

 Conrad's list of Vicksburg species, with a few additions, making a total 

 number of one hundred and twenty-two. While a considerably larger number 

 are known at present, the proportional relations to other faunas will probably 

 be little changed when a complete list is at our service. Conrad recognized 

 seven species of mollusks as common to the Vicksburg and the Jacksonian; 

 three more are known to me. This is less than nine per cent., and it is quite 

 possible that this proportion will be diminished when the whole fauna of the 



