486 Reviews — Barrande*s Silurian Cephalopoda. 



Distribution of the Cephalopoda in Silurian Countries. 



By Joachim Barrande. 



(Extrait du Syst. Silur. du Centre de la Boheme. Vol, II. 4me serie, pi. 351-460.) 

 Prague, 1870. 8vo. pp. 480. 



WE have already directed the attention of our readers to M. 

 Barrande's great work on the Cephalopoda of Bohemia. (See 

 Geol. Mag. 1866, Vol. III., p. 32, and 1867, Vol. IV., p. 322.) In 

 the present volume M. Barrande has prepared, with the most 

 laborious care, a summary of the whole of the vast array of facts 

 and details relating to the geographical and geological range of the 

 Cephalopoda in Silurian countries, and presents us with his de- 

 ductions therefrom. 



M. Barrande excuses himself for the space which he has occupied 

 in the consideration of the Cephalopoda, by showing how vast was 

 their geographical range in Silurian times, and also because they re- 

 presented (if we except the scanty remains of fishes in the older 

 palaeozoic rocks) almost the highest class of living organisms. In 

 the earlier Silurian stages (Fauna II. of Barrande), the Cephalopoda 

 were certainly the dominant class, and it was only towards the close 

 of that great series of deposits that their reign was disputed by the 

 earliest Fishes and the great larval-like Crustaceans of the genera 

 Pterygotus and Tlurypterus. 



Upon the question of the comparative strength of the two classes, 

 the MoUusca and Crustacea, when tested by the relative fecundity of 

 the two groups, M. Barrande seems disposed to divide the palm 

 between the Cephalopoda and the Trilobita, which appear to have 

 been equally innumerable. 



But in organization and in relative age, the Trilobita are pre- 

 eminent. For in the Primordial zone (Fauna I. of Barrande), they 

 represent nearly the entire fauna, whilst not a trace of the Cephalo- 

 poda has as yet been met with in these earliest stratified rocks. 



In the Upper Silurian stages, the abundance of the Cephalopoda 

 would lead one to expect that they would have been discovered in 

 the Primordial rocks, but such is not the case at present, and it 

 would appear that the Trilobita were really called into existence ages 

 before the Cephalopoda. It is but reasonable, however, to assume 

 that a great break in time exists between the Primordial Silurian and 

 the Tremadoc rocks in which the Cephalopoda first appeared. When 

 the relative numbers of the two great groups are compared, the 

 difference is but very small, thus : — 



Total number of Trilobita, 1677 j ^^ff^^^ ^^^ P^i^°^- 

 ' ( dial zone. 



m , 1 T n /-( 1 1 1-1 onn ( From the second and 



Total number of Cephalopoda, 1622 J ^^^^^ g.^^^.^^ ^^^^^^^ 



Difference, 55 



