PREFACE. 



This work contains an account of forty-tliree species of Copepoda, all parasitic on niala- 

 costracous Crustacea, and all belonging to the same family. When in 1890 I began 

 my study of this group, there were published descriptions of only three species, and mention 

 had been made of a fourth. Two more have been since described and a seventh named, 

 but not described; so that until now (July 1897) only five species have been really made 

 known. In the present work I increase this number about nine times, and yet, most 

 likely, my discoveries only extend to one fifth or one sixth or perhaps a much smaller part 

 of the species extant. I have been brought to this conclusion by the consideration that no 

 less than thirty-thi-ee of my species have been found exclusively on Crustacea in the 

 Zoological Museum of the Copenhagen University. What multitudes of these animals are 

 likely to be discovered, when some day the large foieign museums acquire rich collections 

 of non-decapod Malacostraca , and when this material is submitted to a thorough research! 

 On the whole, my studies of late years have given me the impression that of nearly all the 

 Crustacea living on the bottom of the sea — the Decapods excepted — we only know 

 from about half down to a very small percentage of existing species. Especially to the 

 parasitic forms does this apply, and I think one of the most important results of the present 

 work is to show the wealth of a group, which hitherto has occupied only a very diminutive 

 place. It may be added that, in the course of the last two years, I have found on the 

 material brought home from the sea near Iceland and Greenland by the »Ingolf« expedition 

 several new forms which cannot be included in the present treatise, but which will be 

 subjected to fixture examination. 



A chance led me to this study. In dissecting a female of Idofhea marina (L.) I 

 discovered in its marsupium an unknown parasite belonging to the Epicaiidea, and further 

 researches led to the discovery of a number of specimens of this species and of a form 

 nearly akin to it on Edotia nodidosa (Kr.). Both parasites were afterwards described from 



