203 Bibliography. 



American forms with those found in the chalk formations of Europe and 

 Africa. The principal object of this memoir is to present in a tabular 

 form the names of the species found in the American tertiary deposits, 

 and of those detected in the chalk marls of Oran in Africa, Caltasinetta 

 in Sicily, and Egina in Greece. The tables also indicate which species 

 are still living, and therefore show the relations of the present world with 

 the tertiary and succeeding epochs. The full description of the new 

 genera and species is to be given in a forthcoming volume. Among the 

 interesting results of this examination presented by Ehrenberg are the 

 following. 



1st. The remarkable difference which is shown by the American de- 

 posits of marine infusoria from those of Oran, Caltasinetta, dz>c. in the 

 total absence of the calcareous shelled Polythalamia. The siliceous and 

 calcareous shelled animalcules occur together in great numbers both in 

 the present seas and in the chalk marls of Europe and Asia, but no Poly- 

 thalamia have yet been found in any of the specimens of American in- 

 fusoria examined by Ehrenberg,* from which he was at first incorrectly 

 led to suppose that the specimens had been treated with acids to remove 

 the calcareous matter. Ehrenberg remarks that these marine deposits of 

 exclusively siliceous animalcules are not however without analogy, as is 

 shown by the formation of all writing chalk from calcareous animalcules 

 alone, and by the existence of many fresh-water deposits of purely sili- 

 ceous infusoria. 



2d. The comparison of the forms from Richmond, Petersburg, and 

 Piscataway, proves that the infusorial mass at Richmond is composed of 

 at least 112 species, that of Petersburg of 67, and that of Piscataway, 

 Maryland, of 67 also. 



3d. The two deposits of Virginia have about 46 species in common 

 out of 130, or about one third ; Richmond has 66 species which have not 

 been found at Petersburg, and Petersburg 18 not yet found at Richmond. 

 Both of the localities in Virginia agree with that in Piscataway, Md. in 

 46 species out of 155, or about two sevenths. In Virginia are found 84 

 species not detected in Maryland, and in Maryland 21 not found in Vir- 

 ginia. 



4th. Of the 155 North American forms, 60 (52 Polygastrica, 8 Phyto- 

 litharia) agree with those which occur as fossils at Oran, Sicily, and Egi- 



* No Polythalamia have been found in any of the infusorial matters which we 

 have examined from as many as twenty localities in Virginia and Maryland; but 

 as they abound in other beds of the eocene and miocene tertiary, it cannot be sup- 

 posed that they did not also exist during the deposits of the infusorial beds. It 

 appears probable that chemical changes have destroyed the minute calcareous 

 shells without affecting the siliceous ones. That such changes have taken place 

 is shown by the fact that in all the specimens of the infusorial beds which we 

 have seen, casts alone of the shells of the large raoUusks are preserved. 



J. W. B. 



