384 GENERAL SUMMARY TO 



1868 and 1878 been described from the Palaeozoic period; but very many more have 

 been introduced since the date of Dr. Bigsby's publications. 



It is remarkable that the Brachiopoda, so immensely abundant during the Palaeozoic 

 time, should have apparently become so much less numerous in the Permian and Triassic 

 seas, while they became again very abundant, although in somewhat reduced numbers, 

 during the Jurassic and Cretaceous periods. In the Tertiaries they had again materially 

 decreased in number ; and, as we have already shown, are represented at the present time 

 by only rather more than one hundred species. 



It has been clearly ascertained that a small number of genera and species have passed 

 from one or more systems or formations into those that follow ; and this will be seen by a 

 glance at our Tables, in which the general distribution of the genera in time has been given 

 with as much accuracy as the present state of our knowledge upon the subject will permit. 



What wonderful changes have taken place during the incalculable number of ages 

 in which reproduction and extinction of a large number of genera and thousands of 

 species have taken place ! Some few only of the primordial or early created genera, such 

 as Lingula> Distinct, Crania, Waldheimia, and Rhynchonella, have, as. Darwin would 

 say, fought their way and struggled for existence with but small, if any, alteration of 

 shape and character throughout the entire sequence of geological time. By far the 

 larger number of genera were destined to a comparatively ephemeral existence, while 

 others had a greater or less prolongation of reproduction. 



In a most instructive work by Prof. A. Gaudry, Member of the Institute of France, 

 entitled ' Les enchainements du monde animal dans les temps geologiques : Fossiles 

 primaires;' 1883, 1 the author remarks (at p. 29C), "One of the most curious results of 

 palaeontological study has been to show that each one of the epochs of the world has had 

 its own peculiar development. It has had forms which have been specially designed for 

 it ; with it they began their reign, with it their reign came to an end. This will be seen 

 on glancing at the subjoined table, wherein I have indicated the path which the deve- 

 lopment of one part of the primary animals has followed. I have represented each 

 group by a branch " (see next page), " which I have drawn more or less thickly clothed 

 with leaves according as the development has been greater or less." 



In the " Compte-rendu sommaire des Sciences," for the 7th of May, 1883 ('Bulletin 

 de la Soc. geol. de France,' 3 ser., vol. xi, p. 439), we find a resume of his views by 

 M. Gaudry himself. 2 



1 A good brief review of Prof. Gaudry's work, ' Evolution of Life in Palaeozoic Times, 1 is published in 

 the ' Geol. Mag.,' new series, decade 3, vol. i, p. 32, 1884. 



2 M. Albert Gaudry referring to the importance of noting facts derived from the study of Primordial 

 or Palaeozoic fossils, that are beginning to throw a little light on the plan of creation, said, " We do not 

 know from whence were derived the Cambrian animals, but it is difficult to deny that there exists some 

 connection between them and the succeeding Silurian beings, and between the last and the Devonian, 

 and so on. The examination of the primordial fossils leads me to admit passages from one species 

 to another, of genera to genera, and families to families ; but that to remain within the complete 



