THE GENUS ARACHNACTIB 
J. PLAYFAIR McMURRICH 
Professor of Anatomy in the University of Toronto 
FIVE FIGURES 
In 1846 M. Sars instituted the genus Arachnactis for a free- 
swimming Actinian which he found in the autumn and winter at 
Floroe Island, off the coast of Norway, and which he named 
Arachnactis albida. Since that time the species has been fre- 
quently taken in the waters to the north of the British Isles, and 
has been especially studied by Boveri (1890), Vanhoffen (1895), 
Fowler (1897) and E. van Beneden (1898). 
In addition to this type species, three others have been assigned 
to the genus. In 1862 A. Agassiz captured, at Nahant, a form 
which resembled that described by Sars in many respects, but 
at the same time showed sufficient differences to warrant its being 
regarded as a distinct species. Agassiz named it A. brachiolata; 
it has since been taken at Newport, at Wood's Hole, and at Casco 
Bay, on the Maine coast (Kingsley, 1904). 
A third species was first described by Mcintosh (1890) from a 
single example captured in the Bay of St. Andrews, Scotland. 
It seems probable that this is the same species as the A. albida 
recorded by Bourne (1890) as occurring off the south-west coast 
of Ireland, and stated also to be not uncommon at Plymouth. 
At least, this is the opinion of Fowler, who subsequently studied 
examples from Plymouth and who bestowed on the species the 
name A. bournei. The same form was also studied by Van Bene- 
den (1891). 
Finally, among the pelagic Actinians obtained by the ''Siboga" 
during her voyage in the Malayan Archipelago, I have found a 
fourth species for which I propose the name A. sibogae. 
