﻿iv PREFACE. 



be such, or subsequently proved so, together with abstracts of everything that had 

 been written on each, and records of the occurrence of the species in any British 

 rock. Where the references were made to foreign species, I also copied the original 

 author's figure and description. With this book in hand, I then visited all the 

 museums and private collections of which I had knowledge as likely to contain 

 Paleeozoic Cephalopoda; and of every specimen which appeared to show any 

 character, even though of a well-known species, I took by measurement and 

 careful examination all particulars of size, shape, ornaments, and all other cha- 

 racters, assigning to each specimen a number. I specially sought out the specimens 

 which had been used as types, which for the most part are still accessible, and 

 carefully compared these specimens with all that had been subsequently written 

 about the species, to see how far they coincided. I next copied on to separate 

 sheets the actually observed characters of all the specimens which had been 

 described as belonging, or seemed to belong, to the same species, whereby the wide 

 range of variation which must be allowed under the latter title came out, and the 

 best mode of grouping the forms was suggested ; and where any doubt existed, 

 I revisited the museum or collection, or in most instances was able to borrow the 

 specimens for comparison. In the description of the species a single specimen has 

 been described as the type, except in those referred to Bohemian forms, of which 

 M. Barrande does not indicate which he considers as such, and the other specimens 

 referred to the same " species " are grouped round it as best they may be. The 

 work thus includes a description of every known specimen so far as it presents any 

 available characters, or as I have discovered them. The total number of well- 

 characterised specimens examined is about 2000, referred, as will be seen, to 

 143 species. This method would become too tedious to be possibly applied to 

 the infinite number of individuals of the Jurassic forms, but it seems to me the 

 only justifiable one with fragmentary relics such as those of the Silurian. 



I have to return my sincere thanks to the various curators of the museums 

 and owners of the collections for their kindness in allowing me to examine and 

 borrow their treasures, of whom I must mention Sir A. Ramsay, Mr. Etheridge, 

 Dr. Grindrod, Prof. Hughes, Dr. Woodward, Prof. Boyd Dawkins, Mr. Cocking, 

 Prof. Geikie, and Prof. Hull, the Council of the Geological Society, and the Com- 

 mittee of the Cardiff Naturalists' Society, as having rendered me the greatest aid. 



J. F. BLAKE. 



Nottingham, December 1881. 



