306 Viscount cI'Archiac and M. de Verneuil 



We have already stated, that the object of Professor Sedgwick and Mr.Murchison's 

 memoir is to give a detailed account of the proofs in Western Germany and in the 

 neighbouring countries of the equivalents of the Silurian, Devonian, and Carbo- 

 niferous systems which are so finely developed in England, and particularly the beds 

 representing the Devonian system ; for the other two were already well known, al- 

 though not distinctly limited. The journeys performed by one of us with Mr. Mur- 

 chison in various parts of Russia subsequent to the first construction of our tables 

 have afforded us the means of so materially improving them, and of enlarging our 

 general views, that with the approbation of that author we have interpolated some 

 of the chief results of the Russian expeditions in the following pages ; thus antici- 

 pating in some degree what will hereafter be brought before the public in a separate 

 work by Mr. Murchison, M. de Verneuil and Count A. Keyserhng. This table, 

 which forms the third part of our memoir, is extracted from the 'Species general de 

 la Faune des Terrains Anciens,' which we are at present occupied in completing. To 

 each species we have added a synonymy, which, although not fully extended, will 

 always suffice to remove all uncertainty about it. We have also carefully avoided 

 citing any localities unsupported by our own observations or by undoubted autho- 

 rities, and we have been equally careful in referring each species to its proper bed, 

 whether exclusively belonging to the Devonian system, or whether represented at 

 the same time in one of the other two systems, or in all three at once. 



PART I. 



A General Survey of the Fauna of the Palaozoic Rocks. 



When the development of organized beings in each formation or great system of 

 rocks is studied on a sufficiently extended scale, changes more or less distinct may 

 be observed as the inquirer proceeds in certain directions ; and these changes are 

 equally evident whether the system be considered in the direction of its vertical 

 dimensions, that is, in the order of the successive beds, or in the direction of its 

 horizontal or geographic extent. In the latter case the modifications presented 

 by the fauna of the system are comparable to what may be observed at the 

 present time, not only as regards animals which live in different latitudes, but also 

 as regards those which are found upon continents or in seas more or less distant, 

 but placed under the same parallel. Already one of us has endeavoured to dis- 

 cover the law, coBteris paribus, according to which these various changes were 

 effected in the tertiary and secondary deposits, and the details into which we shall 

 enter upon the animal organization of the ancient beds, tend to confirm that law 

 relating to the distribution and the modifications which species undergo in the 

 same system of deposits*. 



• Mem. de la Soc. Geol. de France, t. iii. p. 291 ; Bull. t. x. p. J 68, and t. xii. p. 43. 



