PREFACE. 



IN the following pages I have adopted in great part 

 the general arrangement of M. Milne Edwards, and have 

 adhered almost exclusively to the terminology used by 

 him in his classic work on the Crustacea. Some com- 

 parative anatomists may object to many of the terms 

 employed as not agreeing with their ideas of Horno- 

 logies ; but I have preferred using terms sanctioned by 

 an authority such as M. Milne Edwards, though perhaps 

 in some cases erroneous, to devising others which might 

 be liable to the charge of still more serious mistakes. 



With few exceptions, the figures of the species of the 

 Branchiopoda and Lophyropoda have been drawn from 

 living subjects either by myself or by Mr. Wing, who 

 has devoted much time and labour in illustrating this 

 work. Those of the Caligidae and Lerneadoe have been 

 done by Mr. Wing exclusively, and from specimens 

 preserved in spirits, most of which have been kindly 

 placed in my hands for the purpose by W. Thompson, 

 Esq., of Belfast, to whose liberality I have much pleasure 



