THE BEITISH CAMBEIAN TBILOBITES. 



INTRODUCTION. 



The ' Monograph of British Trilobites,' which was begun by Salter in 1864, 

 and the completion of Avhich was interrupted by his death in 1869, includes 

 descriptions of the families to which he assigned the names Phacopidas, Cheiruridre, 

 Calymenida3, and Asaphidre. The forms with which he had dealt were, therefore, 

 for the most part from the Ordovician and Silurian systems. The Carboniferous 

 species were entirely untouched, and only one or two from the Cambrian and 

 Devonian beds were described. Dr. Henry Woodward has since completed a 

 Monograph of the Carboniferous Trilobites of Britain and Mr. Whidborne has 

 described some of the Devonian species, but the Cambrian forms have received no 

 further attention in the publications of the Palgeontographical Society. 



The long delay, however, has not been without its compensations. A mono- 

 graph prepared in 1869 could have been no more than tentative, for at that time 

 the rich material existing in the Cambrian of Scandinavia and Russia had been but 

 imperfectly described and figured, and the specimens from our own beds are in 

 many cases so extremely fragmentary and distorted that they could not of them- 

 selves furnish a firm foundation for the critical discrimination of species. It is on 

 this account that so much confusion exists as to the meaning of the specific names 

 which have been already employed in Britain. 



In the following pages I have attempted, by means of a careful comparison 

 with the much more perfect material available in Eastern Europe, to reduce our 

 own species to order. But, as many of the Scandinavian forms are even now but 

 poorly represented by published figures, I could hardly have attempted the task if 

 I had not had the opportunity of examining the magnificent collections at Stock- 

 holm, St. Petersburg, and elsewhere. And I owe this opportunity to grants for 

 the purpose from the Trustees of the Worts' Fund of the University of Cambridge 

 and from the Government Grant Committee of the Royal Society, to whom, there- 

 fore, my thanks are in the first place due. 



In the course of my investigations, which, though often interrupted by more 



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