PEEFACE TO THE FOURTH EDITION. 



With regard to tlie present Edition of this work, tlic Aiitlior 

 has only to say tliat he has suhmitted it to a thorough revision, 

 and, to the best of his ability, has brought it up to tlie present 

 standard of our knowledge. As tlie work is strictly elemen- 

 tary, and is intended solely for the use of Junior Students, it 

 has not been deemed advisable to make fundamental altera- 

 tions in its general plan, or to materially change the classifi- 

 cation followed in previous Editions, save in those instances 

 in which there is now a general coiiscmics of opinion. The 

 more important recent additions to our acquaintance with the 

 existing or extinct fauna of the world liave, however, been 

 noticed in the text, and fresh illustrations have been introduced 

 where this appeared to be desirable. 



University, Aberdeen, 

 December 1885. 



