R E F A C E. 



IT is not necessary that I should enter into any 

 explanation of the causes that have delayed the 

 publication of the present work, which was designed 

 and announced several years since ; but I should be 

 ungrateful if I did not acknowledge the enduring 

 patience of the Publisher under trials of no ordinary 

 kind. 



The appearance of this work cannot certainly be 

 accounted premature. Twenty-one years have elapsed 

 since the second edition of Dr. Johnston's ' History 

 of British Zoophytes ' was published ; and during that 

 period the whole aspect of his favourite science has 

 changed. His classification of the Hydroida has long 

 been in great part obsolete, while the number of known 

 species has been almost trebled since he wrote. Like 

 his predecessor, Ellis, he rendered in his day invaluable 

 service to Zoophytology, and gave an impulse to the 

 study of it, of which we are now reaping the fruits. 

 It should be added that there is a charm in his work, 

 which does not become obsolete with its science ; it 



