INTRODUCTION. 



NOMENCLATURE. 



Before entering upon the description of the structure of the many forms which I 

 have to elucidate, it is necessary that the system of nomenclature which I have adopted 

 should be clearly set forth and understood. It is the same as that which was used by 

 Professor Westwood and myself in our History of the British Sessile-Eyed Crustacea, 

 and which has since been extensively employed by naturalists. 



I have invariably adopted the terms proposed by others when they appeared to 

 possess clear homological value, and have only abbreviated most of those of Professor 

 Milne-Edwards in order to avoid redundancy, — for example, in the terminology applied 

 to the various joints of the oral and ambulatory appendages. Some of the terms 

 in common use I have observed to be a frequent cause of confusion, even in printed 

 descriptions, from their similarity in sound. I allude to the terms " endopodite," 

 " exopodite," " apopodite " and " epipodite," — the last three being applied to branches 

 of the first, a fact which is not at all brought out by their respective names. 



The nomenclature here employed appears to be of universal application to the whole 

 of the Crustacea, and avoids the necessity for roundabout explanation, which so 

 frequently destroys clearness of description. 



In the definition and diagnosis of species I have confined myself to the systematic 

 terms as given in the accompanying table, but when writing where less exactitude was 

 necessary, I have generally used the more popular expressions. 



The nomenclature of the parts is shown in the accompanying woodcut (Fig. I.) of 

 an ideal Macrurous Crustacean, in which the appendages are represented of several 

 characteristic forms. 



