PRESTWICH — BRITISH AND FOREIGN TERTIARIES. 



129 



Calcaire grossier in the east of the Paris basin, expand as they range 

 westward, giving indications of the development which they attain 



136 species of which they consist there have only been 14 identified as common 

 to the French and EngUsh series. This is shown in the following Table. 



Bracklesham Sands and Calcaire grossier *. 



Genera common to the two areas. 



Total number of 

 species. 



Species 

 common 

 to both 

 countries. 



France. 



England. 



N autilus 



2 

 6 

 9 

 3 

 5 

 5 



12 



3 



8 



15 



13 



2 

 4 

 9 

 3 

 5 

 4 

 4 

 3 

 7 

 12 

 16 





 2 

 

 1 

 2 

 2 

 1 

 1 

 2 

 

 3 



Ancillaria 



Bulla 



Cassidaria 



Conus 



Cypraea 



Dentalium 



Rostellaria 



Scalaria 



Lucina 



Tellina 





81 



69 



14 



So in the next period another 10 genera with a total of 121 species show only 

 13 in common. 



Barton Clay and Sables Moyens. 





Genera common to the two areas. 



Total number of 

 species. 



Species 



common 



to both 



countries. 



France. 



England. 



Cypraea 



3 



16 



2 



8 



5 



3 



17 



12 



2 



2 



2 



13 



3 



4 



5 



4 



16 



12 



3 



3 





 5 

 



1 

 



1 



3 

 3 

 

 



Fusus 



Marginella 



Melania 



Mitra 



Oliva 



Pleurotoma 



Voluta 



Crassatella 



Pecten 





70 



64 



13 



The same remarks may be made of some of the Zoophytes : thus there are 

 four specise of Turbinolia in the Sables moyens, and five in the Barton Clay, all 

 considered different. Of ten Serpulce on one side and five on the other, none 

 agree. 



The species seem to be representative species ; yet would I ask palaeontologists 

 to consider in such cases, when the definite synchronism of certain strata is esta- 

 blished upon structural and general grounds, how far some of these apparent dif- 

 ferences in the species may be varieties brought about by the great differences of 



* The number of French species are those given by M. Graves. 

 VOL. XIII. — PART I. K 



