FUCHS — EOCENE FOSSILS. 13 



attained during the Silurian period the maximum of its relative de- 

 velopment—so much so that Prof. J. D. Dana has given to that period 

 the name of the " Age of Mollusks." 



This comparison of the Palaeozoic systems, which regards them as 

 units, does not assist in settling the law of the development of ani- 

 mal forms, because the successive systems, in aR probability, repre- 

 sent very unequal lengths of time. M. Earrande considers that for 

 the determination of the true laws of the numerical increase and de- 

 crease of animal forms coexisting on the globe, it is indispensable to 

 subdivide the duration of each system into units of equal time, just 

 as each country is subdivided into units of surface for the purpose 

 of comparing the density of their population. 



Taking the general fauna as units, the third Silurian fauna pre- 

 sents the appearance of the maximum development of animal forms 

 during Palaeozoic times. It is especially the third fauna of Bohemia 

 which contributes to establish this numerical preponderance, by its 

 contingent of no less than 1^400 species of that age. Moreover, 

 starting from the third fauna, a marked decrease is observed in the 

 number of species, either in ascending to the upper horizon, or in 

 descending to the lower. In every case, the Permian, or Dyas, 

 fauna presents an incontestable and very pronounced minimum, to 

 which the Devonian and Carboniferous faunas gradually lead. This 

 minimum fauna indicates, by its extreme numerical reduction, the end 

 of the Palaeozoic era, although it contains the representatives of nearly 

 all the fundamental types of the animal series. On the other side, 

 immediately below the second fauna, which is distinguished as much 

 by its specific richness as hj the appearance of most of the generic 

 types, another minimum is found in the Primordial Silurian fauna. 

 But this minimum is characterized by the extreme predominance 

 of a single class of animals — the Crustacea — which is itself repre- 

 sented almost exclusively by Trilobites. In the midst of these 

 Crustacea appear some rare forerunners of the Mollusca and 

 Eadiaria. [A. S.] 



On Eocene Fossils from Kiew, W. Russia. By T. Fucns. 

 [Proc. Imp. Geol. Inst. Vienna, June 4, 1867.] 



A SERIES of Eocene fossils from Kiew has lately been transmitted 

 for determination to the Imperial Museum of Vienna by M. C. 

 Theofilaktoff, Professor of Geology at the University of Kiew, toge- 

 ther with a map and section. The whole Tertiary deposit rests 

 partly on Cretaceous strata, and parly on Granite (" Steppe-Granite"). 

 Prof. Theofilaktoff remarks of these fossils that they bear a greater 

 resemblance to those of Volhynia than to any occurring in the Lower 

 Tertiaries of Kiew. 



The following are the fossils which have been determined from, 

 the several divisions of the Kiew Tertiaries : — 



