AKNIVEESAKT ADDRESS OP THE PRESIDENT. Hii 



Mollusca found in the Chalk, 80 (of which 19 make their first 

 appearance at that period) are living at the present day. At the 

 same time it is not in the deep Atlantic, but rather on its warmer 

 coasts, that we now find the widest dispersion of this group of cre- 

 taceous genera. 



These constitute the main points of resemblance. Striking as they 

 are, their limits are confined ; and, on the other hand, the divergences 

 are great. The great feature of the Chalk-fauna is the abundance of 

 Cephalopods and its large reptiles, so very few genera of which have 

 descended to present times. The relative distribution of genera of 

 the principal Invertebrata was, according to D'Orbigny *, before the 

 late discoveries, approximately as under : — 



Number of genera. 



In the Extinct j . . 



White Chalk, with tlie Chalk. -i^ivmg. 



Cephalopods 13 12 1 



Gasteropods 41 9 32 



Lamellibranchs .52 11 41 



Brachiopods 10 3 7 



Echinoderms 34 27 7 



150 62 88 



"With the Cretaceous series disappear the many genera of Cephalo- 

 pods allied to Ammonites which range through the Triassic and 

 Jurassic formations, together with the Eudistes, so peculiar to the 

 Chalk period. 



The MoiLTJSCA of the deep Atlantic are stiU undergoing investi- 

 gation at the hands of Mr. Gwyn Jeffi-eys. Enough, however, is 

 already known of the remarkable results to form some opinion of 

 its great value in a geological point of view. The total number now 

 dredged may probably exceed 300 species. Of these, 86 species 

 have been recognized and are noticed in the Reports now published. 

 A very large number are altogether new. With the aid of Mr. 

 Jeffreys, I have drawn up the following lists, which will serve to 

 show the light which may be thrown on the palasontology of our 

 more recent Tertiary strata by these inquiries. Of the 86 deter- 

 mined species, 67 were known before as living, though chiefly as 

 high Northern and Arctic species (while the wider range of some 

 few of the species is very remarkable), and 19 are fossil species 



* Paleontologie at Geologic stratigraphiques, vol. iii. § Terrain Senonien. 



