8 



GEOLOGICAL MEMOIRS. 



shell, the curvature of the edge of the septa, &c. Both genera have 

 species with individuals measuring more than 25 centim. in diameter, 

 — a size that could be scarcely expected for the period of their first 

 appearance on the earth's surface. This agreement between Nautilus 

 and Goniatites is of double importance, since it proves the transition 

 not only between these two genera, but also between the two families 

 of Nautilidce and Ammo/iitidce ; and it is worthy of notice that this 

 transition existed at a time when the latter family was represented 

 only by a single genus, and whilst the former presented its greatest 

 development both in genera and species. 



M. Barrande proceeds (p. 5-12) to review the several genera of 

 the Cephalopods of the Bohemian Silurian rocks, succinctly descri- 

 bing the characteristics of each type, with notices of some of the 

 species, and outlines (in an accompanying lithograph plate) of some 

 of the most interesting forms. The geological distribution of these 

 Cephalopods is exhibited iti the accompanying Table. 



Table of the JDistrihiition of Cephalopoda in the Silurian Rocks 

 of Bohemia. 





Genera. 



Lower Division. 



Upper Division. 



Stages 

 A. B. 



stage 

 C. 



1st Fauna. 



Stage 

 D. 



2nd Fauna. 



stage 

 E. 



Stage 

 F. 



stage stage 

 G. H. 



Az oic. 



3rd Fauna. 



1 



2 

 3 

 4 



5 



6 



7 



8 



9 



10 



Nautilus 













■■ 









Lituites 









Gyroceras . . . 









Trochoceras... 









. 











Cyrtoceras . . . 









1 ^ 1 



'S 



_o 



"3 

 o 

 1 I 





1 ^ 1 



'5 — 

 1 1 



Gomphoceras 

 Phragmoceras 

 Ascoceras 











































I 



This tabular view, says M. Barrande, shows, what I have else- 



