n INTRODUCTION. 



BIBLIOGRAPHY. 



It is unnecessary to give any extended list of works on 

 the Hydroida, as those who are studying the literature of 

 the subject will find full information in the ' Bibliographia ' 

 by Agassiz, published by the Ray Society, the supple- 

 mentary volumes by Carus and Engelmann (Bibliotheca 

 Zoologica, 1848 to 1860), and the invaluable ' Record of 

 Zoological Literature/ issued annually under the editor- 

 ship of Dr. Giinther. A good list of Memoirs published 

 subsequently to 1860 is prefixed to the ' Catalogue of 

 North American Acalephee/ by Alexander Agassiz ; while 

 the well-known journal,, the ' Archiv fur Naturgeschichte/ 

 contains a critical review of the Coelenterate literature of 

 each year by Prof. Leuckart, which is of the highest value 

 to the student. In Prof. Greene's < Manual of the Coelen- 

 terata ' there is also a list of some of the principal works 

 and papers on the Hydroida. 



A selected list, which may answer the general purposes 

 of the student, is given at the close of the present work. 



DICHOTOMOUS TABLES. 



The following Tables are added to enable the student at 

 once to refer any species which he may find to its place. 

 It must be clearly understood that they do not represent 

 natural affinities and relationships, but are a purely arti- 

 ficial contrivance to save time and somewhat wearisome 

 labour. Having determined by their aid the genus to 

 which his zoophyte belongs, the student should refer to 

 the Synopsis of Families and Genera at the close of the 

 Introduction to learn its position in the natural system. 



The characters on which the dichotomous division is 



