PREFACE 



TO THE SECOND EDITION. 



IN preparing a second edition of this work for the press, I 

 have endeavoured to incorporate in it the species which have 

 been discovered since its first publication ; to correct the no- 

 menclature and synonymy throughout ; to amend the descrip- 

 tions, and to add such additional particulars of the habits and 

 external anatomy of the species as have come to my know- 

 ledge. It was deemed unnecessary to enter into minute 

 details of the internal structure of these animals ; and the 

 intimate anatomy of their tissues and organs has been entirely 

 omitted, for I am convinced that it is now time to separate 

 such details and discussions from descriptive natural history. 



To aid my wish to make this history more complete, my 

 friends have come forward with zealous alacrity, and it would 

 need strong words to convey to them, and to my readers, the 

 sense I have of the value of their co-operative assistance. That 

 assistance has, I trust, been acknowledged in its place, it 

 would pain me to find any omission, but here I would, on 

 parting, again tender my thanks to William Thompson, Esq., of 

 Belfast; to Professor Edward Forbes; to Mr. A. H. Hassall; to 

 Mr. C. W. Peach; to the Rev. David Landsborough ; to Lieut. 

 Thomas, R N. ; to Mr. Cocks of Falmouth ; to Mr. Couch ; 

 to Mrs. Griffiths, Miss Dale, and Miss Ellen Forster ; to 

 Mr. Bean; to Professor John Reid; to Professor Allmaii; 



