Introduetion. 
In the following monograph I intend to give a systematic survey of Northern and 
Arctic Alcyonacee, particularly those which are represented in the collection of the 
Swedish State Museum in Stockholm. This paper will therefore belong to the series of 
monographs on Northern and Arctic Invertebrates in the Swedish State Museum, edited 
by Professor Dr. HJ. THÉEL. In conformity with the programme for this series, I have 
paid special attention to the geographical distribution of the material investigated, 
i. e. the situations and depths of the localities where the specimens were found. 
For further details regarding the scientific expeditions by which these collections 
were brought home, see THÉEL, Sv. Vet. Ak. Handl. Bd 39. 
I have taken the very exact investigation of KÖUKENTHAL as the basis of the syste- 
matization of the group under consideration. The results obtained by this research, 
however, differ in certain respects from those of KÖKENTHAL. I have, like KÖKEN- 
THAL, paid particular attention to the structure of the canal-system and of the spicules, 
as well as to the shape of the colonies, and also to the formation of a calyx. I am con- 
vinced that, by means of such a study, it is possible to construct a system for the group, 
but it is also necessary to investigate with exactness the degree to which these charac- 
teristics can be taken as distinctive features. 
I have much pleasure in acknowledging my gratitude to Professor Dr. HJ. THÉEL, 
on whose initiative this investigation was commenced, for much help and encourage- 
ment. I am also indebted to Professor Dr. A. WIRÉN, of Upsala, for the kind interest 
he has taken in my work and for many valuable suggestions. 
Several distinguished zoologists have kindly supplied me with valuable material 
for the investigation. My sincerest thanks are therefore due to M. Dr. RICHARD, Direc- 
teur L'institut oceanographique, Monaco, Herrn Professor Dr. BAUTER, Direktor Kal. 
Museum fär Naturkunde of Berlin, Herr Professor Dr. H. JUNGERSEN, of Copenhagen, 
and Herr Konservator Dr. BJERKAN, of Bergen. 
I also take this opportunity of thanking Mr. LILJEVALL for his skilful assistance 
with the illustrations. 
