INTRODUCTION. 



f MHE present Revision of the Echini has been in my hands for the 

 -*- greater part of six years ; its publication has been delayed from 

 the impossibility of examining a large number of the original specimens 

 of the principal writers on the subject. Its earlier appearance would 

 have been useless without such an examination. This was made during a 

 recent visit to Europe, when the species of Echini (with very few excep- 

 tions) described during this century were examined, and carefully com- 

 pared with specimens sent from the Cambridge Museum to Europe for 

 that purpose. 



Of many of the specimens we have, of course, only the tradition that 

 they are the originals made use of by various authors ; this is especially 

 the case with the types of the older authors in the Jarclin des Plantes and 

 in the British Museum ; but as no one has recently attempted to make 

 direct comparisons of the numerous species described independently, it is 

 not astonishing that when such a comparison is made the number of spe- 

 cies distinguished should be found to be so small. 



To Dr. John E. Gray and the late Dr. Baird of the British Museum I am 

 indebted for giving me every possible facility to examine the collections 

 of the British Museum, containing the t}^pes of Dr. Gray's Catalogue of 

 Recent Echini, of his papers in the Proceedings of the Zoological Society 

 of London, in the Annals and Magazine of Natural History, in the Annals 

 of Philosophy ; to Dr. P. L. Sclater for his kind assistance in hunting up 

 the types formerly in the collection of the Zoological Society; and to Dr. 

 Charles Stewart for his aid while working in the rooms of the British 

 Museum. 



The collection of Echini made by Professor Percival E. Wright at the 

 Seychelles Islands was examined at Dublin. Dr. Carpenter and Mr. Jeff- 

 reys allowed me to examine, in company with their colleague, Professor 

 Wyville Thomson, the Echinoderms, collected in the different cruises of the 

 English Deep-Sea Dredging Expeditions, which had been brought together 



