ACTINIARIA 



161 



the explanation of such a mistake is very simple, because these genera display a great variation in some of 

 their anatomical characters, as is evident from the description given here. Only through a study of the sting- 

 ing capsules it has become possible to lay a sure foundation for future works on this family. It has namely 

 been proved that the stinging capsules are good characters of the species, and mostly also of the genera. In 

 my paper of 1902, in which I have described Rhodactinia crassicornis and mentioned Tealia lofotensis and 

 coriacea, I made myself liable to some mistakes because I had not examined the size of the stinging capsules 

 at the time when I wrote my paper. I have for inst. in the description confounded Cribrinopsis with some 

 Urticina crassicornis, not provided with reproductive organs but with embryos in the coelenteric cavity. 

 In order to show the difference in the size of the nematocysts of the tentacles (a) and of the actino- 



90 



to 



A B * C D 



Textfig. 170. Diagram of the size of the nematocysts in some Cribrinids (compare the text!) 



pharynx (b) of some examined Cribrinids, I have in the textfigure 170 put together the length of the 

 nematocysts. The size of the nematocysts in Cribrina stella (A) is measured in 19 specimens, in Cribrina 

 spetsbergensis (B) in 12, in Cribrinopsis similis (C) in 23, and in Urticina felina crassicornis (D) in 30. The 

 length of the lines represents the variation in /j of the length of the nematocysts in the different specimens. 

 While the length of nematocysts in Cribrinopsis similis is about the same in the tentacles and in the 

 actinopharynx, it is more or less different in the other species ; the difference is especially great in Urticina 

 felina. As the table shows, these species are easily identified by examinating the size of the nematocysts. 

 I especially wish to point out how important the nematocysts may be to the systematizing, and to call the 

 attention to the fact that the size of the nematocysts is as good a systematic character as any other. 



Urticina felina (I,.) Marenz. 



PI. 4. Figs. i -4. 



Diagnosis: Number of tentacles and mesenteries unto about 160. Tentacles in contracted state 

 longitudinally sulcated. Nematocysts of the column smaller than those of the tentacles, those of the actino- 

 pharynx from two and a half unto three times larger than the larger nematocysts of the tentacles. Nemato- 



The Ingolf-Expedition. V. 9. 21 



