388 NATURAL SCIENCE. Dec. 



in Schleswig, i6 in Bohemia, and lo in Westphalia. Combining, 

 therefore, this evidence with the changes in the Hthological 

 character of the Upper Cretaceous rocks, viz., the more sandy 

 condition of the strata in Bohemia and Saxony, and their more 

 calcareous character in Schleswig and Riigen ; and taking into 

 account the far greater richness of the echinoderm fauna in the 

 northern provinces of Germany, it should be conceded that the 

 Mollusca displayed a definite arrangement and grouping in Cretaceous 

 times, the Gastropoda being richer in species nearer shore, the 

 Dimyaria becoming more abundant in depths beyond the littoral 

 boundaries, while in the deep sea Monomyaria were decisively pre- 

 dominant. 



We are consequently led to the conclusion that in Upper 

 Cretaceous times the continental shore-lines and oceanic areas had a 

 molluscan fauna subject to laws of distribution like those of the 

 present day ; and that the Gastropoda, Scaphopoda, and Pelecypoda 

 occurring in the white chalk of northern Germany belong to genera 

 which at the present day range in depth up to or over a thousand 

 fathoms. 



The preceding discussion has chiefly dealt with beds occurring 

 in Germany, all deposited at the same period, but under dissimilar 

 conditions. Let us now turn to England and trace the change in the 

 molluscan fauna, not in space, but in time, and mark the variation 

 displayed during the changing conditions at the close of the 

 Cretaceous period. 



Evidence is by no means wanting of the existence of a very rich 

 molluscan fauna at tae beginning of the Upper Cretaceous period, and 

 this has already been referred to in the mention of the Blackdown 

 deposits. For the sake of comparison with the German data, a list, 

 based on a personal study of our national collections, may be given. 

 Gastropoda, 25 species : the principal genera are Turbo 4, Natica, 

 Littonna, Aporrhais, and Fusiis 3 each, Tnrritella and Rostellavia 1 each, 

 other genera bemg Mnvex and Dcntalium. Pelecypoda, 64 species : the 

 principal genera are Trigonia 12, Cytherea y, Nucula, Astarte, a.nd Exogyra 

 4 each, Cyprina, Cavdium, CncuUaa, and Mytilus 3 each. For the same 

 period in Germany the principal types were : Gastropoda ; Tvockus 10, 

 Rostellavia 6, Tnrritella and Pleurotomavia 3 each, but the tropical forms, 

 Voluta, Conns, and Strombus, were already sparsel}^ represented : Pelecy- 

 poda ; Pecten 18, Lima, Area, and Mytilus 8 each, Inoceramus 5, Gastro- 

 chcBna, Cavdium, Cyprina, Nucnla, and Avicula 3 each. It appears to 

 follow from these data that the minor life-provinces of the Mollusca 

 were already well marked ovit ; the result of subsequent changes was 

 on the one hand, to accentuate the tropical character and increase the 

 specific richness of the German fauna, and on the other to reduce the 

 molluscan variety in the English area. 



In the higher strata of the Upper Greensand of England the 

 change becomes well marked. Plenvotomaria now takes the lead among 



