PRELIMINARY REMARKS. 5 



determinations have tended to add considerable confusion to our notions . as to the 

 repartition of species in the two respective systems. 1 



It is well known that the careful stratigraphical and palseontological investigations 

 made in the vast Silurian system by Sir R. Murchison, Mr. Barrande, M. De Verneuil, 

 and others, as well as those conducted throughout the Jurassic, Cretaceous, and Tertiary 

 periods by different competent naturalists, have nowhere exhibited that wholesale mixture 

 or general longevity in time or existence of the numerous species which we should be led 

 to believe did take place in the two above-named epochs. 2 Our researches have hitherto 

 unmistakingly led us to repudiate such an assumption, and to urge us on the contrary to 

 believe that the law which has regulated the vertical distribution of animal forms did not 

 differ in those extended palaeozoic systems any further than it did in those of newer or of 

 more ancient date. M. De Koninck states "that he has succeeded in tracing, in the 

 Carboniferous formations of England and Scotland, two great different faunas ; the one 

 corresponding to the Carboniferous fauna of Vise and Bleiberg, the other to the fauna of 

 the Tournay coal basin. These two faunas, although contemporaneous, are said to be 

 nowhere found coexistent." 3 But it will be preferable to reserve what we may have to add 

 on this subject until the completion of the descriptions of the species which will compose 

 the present monograph. 



So variable do we find the individuals of the same species to be, especially when 

 our examinations are not restricted to a small number of examples (and this more so 

 in certain forms than in others), that we are sadly at a loss in many cases to know 

 how to define and where to confine the limits of variety, and even how to appreciate 

 the value of the characters which are to be brought forward in the discrimination of two 

 different, although closely allied forms. There generally, however, exists a certain fades 

 or peculiarity in each combination of individuals that leads the experienced palaeontologist 

 to separate, with more or less success, forms- which could hardly be identified if unaccom- 



1 These erroneous identifications with Devonian species were published in 1844, and I believe tbat 

 Professor M'Cov himself repudiates at present the larger number so inscribed ; but I have felt myself 

 compelled to draw attention to the point in question, as it is of great importance in our geological and 

 palseontological inductions. The same must be said relative to Mr. Kelly's excellent and most valuable 

 memoir and synoptical table, ' On the Localities of Fossils of the Carboniferous Limestone of Ireland,' 

 published in the ' Journal of the Geological Society of Dublin,' March 14th, 1855, but in which Professor 

 M'Coy's mistaken identifications are reproduced. This most useful work, to which we shall have so often 

 occasion to refer, was published by its author in a great measure to fill up a sad omission iu the ' Synopsis,' 

 in which the localities of almost every species had been purposely omitted. 



2 It is true that, in Professor Phillips's work, * Figures and Descriptions of the Palaeozoic Fossils 

 of Cornwall, Devon, and West Somerset,' a very large number of true Carboniferous forms are described as 

 occurring in Devonshire Devonian strata, such as at Barton, near Torquay, &c. ; but perhaps some of the 

 beds taken as Devonian may be in reality Carboniferous, a point which will require hereafter to be inves- 

 tigated with all possible attention. 



3 ' Proceedings of the Geol. Inst, of Vienna,' 1856 ; 'Quarterly Journal of the Geol. Soc.,' vol. xiii ; 

 and 'Bulletin de l'Academie Royale de Belgique,' vol. xxiii, No. 9. 



