N T I C E. 



I FIND it difficult to express my obligation to my friend, Mr Alexander Agassiz, 

 for the valuable assistance which he has given me in carrying out this under- 

 taking. 



Shortly after the return of the Challenger Mr Agassiz came to Scotland, 

 and we went over the enormous collection together, when his remarkable 

 familiarity with invertebrate forms was of the greatest possible service in 

 selecting and separating the different groups, and preparing them for the 

 specialists to whom they were finally to be consigned. 



Mr Agassiz afterwards undertook the description of the Echinoidea, in 

 which order his personal acquaintance with all known types, recent and fossil, 

 gives him an advantage as an authority over all his contemporaries : without 

 some such special training, it would have been a matter at least of extreme 

 difficulty to decipher the complex relations of the multitude of singular forms, 

 intermediate between the faunw of ancient and modern times, which have 

 been brought to light by the Challenger Expedition. 



In all cases in which the question of nomenclature has been left entirely 

 to myself, I have, after full consideration, adopted the code approved by Mr 

 Strickland's Committee, and successive Committees of the British Association, 

 and especially that part which inculcates the reference of the name of every 

 species to the name of the first post-Linnean describer. My friend and I agree 

 to differ somewhat on these points, and I here take refuge in my former ex- 

 planation, that in such cases I can act only as Editor. 



Several important contril)utions to the natural history of some of the more 

 obscure groups of marine articulata, have been for some years known from the 



