102 



HYDROIIM II 



1913, 1914) that the dimensions may here quite commonly become coarser within the same species as 

 the temperature decreases. In Sertularella polyzonias forma gigantea, this common law has been fol- 

 lowed to an extreme, while the transition forms are comparatively few. That they exist, however, 

 is plainly evident from the present material, where in particular certain colonies from Jakobshavn, 

 Greenland, and all those from Bredebugt take up a doubtful intermediate position. 



Forma gigantea (fig. LIV) is a typical arctic (and antarctic) character form, only exceptionally capable 

 of penetrating into the boreal region. It is extremely common in West Greenland waters, and is also 

 known from East Greenland; occasionally also from the north coast of Iceland. Forma typica, on the other 



iooo m. 1000m 



Fig. LIV. Finds of Sertularella polyzonias forma typica « and forma gigantea + in the Northern Atlantic. 

 In the hatched regions the literature notes a common occurrence of the forma typica. 



hand, is cosmopolitan, and occurs also, albeit less frequently, in arctic waters. In the boreal area, it 

 is particularly numerous in the eastern parts. Both forms belong to the middle parts of the littoral 

 region, and rarely move down into the deep sea region. 



Sertularella Gayi (Lamouroux) Hiucks. 

 1821 Serhilaria Gayi, Lamouroux, Exposition methodique des genre . , . p. 12, pi. 66, figs. 8—9. 

 1868 Sertularella Gayi, Hiucks, A History of the British Hydroid Zoophytes, p. 237, pi. 46, fig. 2. 



Upright, irregular doubly pinnate colonies with distinctly prominent polysiphonic main stem 

 and main branches. The outer branches are almost regularly pinnately branched often with their minor 

 branches secondarily ramified. The outer branches are divided by indistinct oblique joints into short 

 internodia, having on their distal half a large hydrotheca; the hydrothecse are directed alternately to 



