AMMONITES— ZOOLOGICAL, ETC. 



341 



A. Fissicostatus. A. Milletianus. A. Rauliniams. 

 Guersanti. Puzosianiis. regularis. 



Mosensis. quercifolius: tardefurcatus, 



Michelinianus. 



The several preceding lists show that the Gault was more 

 extended than the Neocomien ; it is, notwithstanding, want- 

 ing in the ancient Gulf of the ^Loire, and it is somewhat 

 doubtful in the south-west of France, and as yet only found 

 in the parts adjoining the Proven9al basin. By comparing 

 the several faunas, as I have done in the Neocomien, I find 

 that in the Provengal basin they comprise sixteen species ; 

 in the basin of the Seine, or Parisian basin, twenty-five 

 species ; in the Jura and Savoy, twenty species ; in the Ar- 

 dennes and Meuse, twenty species. These figures, without 

 regarding the faunas, prove a nearly equal division of species 

 in each basin, and furnish an enormous difference between 

 the relative proportions which existed at the Neocomien 

 period. I shall now compare the forms of the four localities 

 with each other. 



1st. In the Provenpal basin, I recognise in the lower beds, 

 three species, one of which, A. nodosocostatus^ is peculiar to 

 them, the others are found in the different basins ; and in the 

 upper beds, thirteen species, eight of which are common to the 

 Parisian basin, seven to the Jura and Savoy, and four to Ar- 

 dennes and Meuse. After these deductions there remain 'but four 

 species {A.AIpinus, Camatieanus^ Roissyanus smd Senequieria- 

 nus) which at present are peculiar to the Proven5al basin, and 

 all belonging to the upper beds. The comparison which I have 

 made is far from furnishing me v^ith the same results as the 

 Neocomien. There are far more common species in the 

 Gault, and everything induces me to believe that at the 

 period of the upper Gault, the Proven9al basin had changed 

 its boundaries ; that it had greater communications with the 



