The paper on the Actiniaria, of which I now present the first part, has been drawn up according to the same 

 plan as my reports on the Ceriantharia and Zoantharfa of the Ingolf-Expedition. The main part of the 

 material examined by myself belongs to the museums in Copenhagen and Stockholm. I have had at my 

 disposal a rather great collection mainly enclosing the forms dredged by R0mer and Schaudinri during 

 their journey around the Spitzbergen, and I have also examined smaller collections from the museums in 

 Upsala, Gothenburg, Lund, Christiania, Bergen, Drontheim, Troms0, Francfort on the Main and Petrograd. 

 I beg to express my best thanks to all, who have supported my work through lending of material. 

 The paper on the Ingolf- Actiniaria will be divided into four sections: 



1) Description of the species. 



2) Survey of the literature with critical notes on the arctic and northern Actiniaria. 



3) Distribution of the species. 



4) Contribution to the anatomy, genealogy and classification of the Actiniaria. 



In the present paper I have described all families occurring in the arctic and northern waters ex- 

 cepting the forms which have been referred to the old family Sagartiidae. 



I have given special attention here to the size and distribution of the nematocysts and spirocysts. 

 As before emphasized by me the stinging capsules are of great importance to the classification. Nearly related 

 genera show great agreement in the appearance and distribution of the nematocysts, and the species are often 

 characterised by the different sizes of these latter, though in many cases the differences are not great. In 

 fact I think that it is impossible to put up a good system of the Actiniaria without considering the stinging 

 capsules. Concerning my statement of the breadth of the stinging capsules I will remark that it is approx- 

 imate. 



