192 THE OCEAN 



and Antarctic have no representatives in 

 intermediate regions and there is a striking 

 similarity in the character of the forms of the 

 two regions. The siphonophor Diphyes arc- 

 tica is bipolar. 



Hydroids. — G. J. Allman states that no less 

 than three British species of hydroids occur in 

 both the northern and southern regions. 

 Perisiphonia filicula is taken at the Azores and 

 in the Australian region ; the northern 

 Grammaria is represented by three species 

 from a comparatively narrow zone of southern 

 latitude. Sertularia operculata is bipolar, and 

 so is Obelia geniculata, a British hydroid 

 taken in the vicinity of Kerguelen and the 

 Falkland Islands. Clemens Hartlaub gives 

 seventeen bipolar species of hydroids. Of the 

 genera of the sub-Antarctic all except three 

 are represented in the Arctic. 



Sponges. — Thenea grayi from the South 

 Australian region much resembles Thenea 

 muricata of the Arctic regions. 



Phytoplankton. — ^H. H. Gran states that of 

 the seventeen species of Arctic oceanic diatoms 

 eight occur also in the Antarctic and are 

 wanting in the intermediate regions. In a 

 private letter Gran writes that it is very 

 difficult to decide from preserved material 

 whether the Antarctic Phceocystis is identical 

 with the Arctic Phceocystis poucheti ; there 



