Reviews — Barrande's Silurian Cephalopoda. 



487 



So that, assuming there may be 55 species of Trilobites found in the 

 Primordial zone in the rest of the Silurian series, the hosts of the 

 Cephalopoda equal those of the Trilobita. 



In the first appearance of the Cephalopoda, it is interesting to 

 notice that they are met with not only in widely separated geogra- 

 phical positions, but also in great generic and specific variety. 



The total number of types in this class is 25, and of these 12 

 make their appearance in the earliest stage of their incoming. (See 

 the following table.) 



The siibjoined Diagram represents the extension of the principal 

 generic types of the order of the Cephalopoda which appeared during 

 the Silurian period.^ 





PAT.^.OZOIO. 













SILURIAN FAUNAS. 



Devonian . 



p 

 o 



OS 

 » 



S 



O 



« 



6 



(2 



MESOZOIC. 





I. 



II 



II. 



III. 





o 



% 



a ' 



3 



o 



6 





PRINCIPAL 



or 

 COSMOPOLI- 

 TAN TYPES. 



1 



a 



u 



1 



3 



o 



1 



> 



o 



3 







1 



bo 

 a 



la o 



Ooniatites 



Oyroceras 



Ascoceras 



Phragmoceras 

 Oomphoceras . 

 Trochoceras ... 







. 



























. '. _ 



-L! 



- 









? 





• 

















-Z. . . — 





Nautilus 















— 







1 



































Of the Secondary or local types one, Bactrites, ranges from the 

 Silurian (II.) to the Devonian. Five, Piloceras, Bathmoceras, Cono- 

 ceras, Gonioceras, Discoceras, occur only in the lower stages of Fauna 

 (II.). Ophidoceras occurs in the Llandeilo and Wenlock stages. 

 Tretoceras occiirs in the Llandovery and in the Ludlow stages. Three, 

 Huron la, Aphragmites, and Qlossoceras., occur only in the Wenlock and 

 May Hill stage, the lowest part of Fauna (III.) ; lastly, three, Herco- 

 ceras, Nothoceras, and Adelphoceras, occur only in the Uppermost 

 Silurian of Fauna (III.) 



In another table (too large to be reproduced here), M. Barrande 

 shows the first appearance of the types, and he observes that in each 

 principal region compared, there is a very great diversity both in the 

 first generic appearance, and also in the numbers met with. Thus 

 in Canada a small Orthoceras first appears at the base of the 

 Calciferous sandstones ; in England a small Gyrtoceras is found in 

 the Tremadoc slates ; in Kussia eight different types are met with in 

 the Orthoceras limestone ; whilst in Bohemia seven types appear 

 together in Bande d 1 of M. Barrande (or Tremadoc ?). 



M. Barrande divides the Cephalopoda into three families, the 

 Goniatidce, the Nautilidm, and the Ascoceratida. The first of these 



1 Taken from Barrande's work (p. 266). 



