HYDROIDA II 113 



Diphasia rosacea should doubtless be regarded as a southern species having a very wide distribution 

 in the southern part of the boreal area (fig. LX). It has been found at several places near Iceland, 

 and is also recorded from the Faroe Islands. Round the British Isles and in the North Sea it is very 

 common, and very frequent between Bergen and Stat on the west coast of Norway. Having also been 

 found in north Norway (Tananger), it will probably likewise prove to be fairly common along the 

 Norwegian coast in the deeper part of the laminaria belt, which is its true home. 



Diphasia attenuata Hincks. 

 1866 Sertularia attenuata, Hincks, On new British Hydroida, p. 298. 

 1868 Diphasia attenuata, Hincks, A History of the British Hydroid Zoophytes, p. 247, pi. 49, fig. 1. 



Upright, often brown-coloured, pinnate colonies with slightly pronounced monosiphonic stem, 

 the lower part often without hydrothecse or branches, and divided into internodia of irregular length; 

 the upper part of the stem has alternating branches, which are in rare cases themselves secondarily 

 branched to a slight degree, and may now and again terminate in tendril-like outgrowths. The branches 

 and the upper part of the stem are indistinctly segmented; each internodium bears a pair of oppositely 

 placed or slightly subalternating hydrothecse. Between two successive branches on the same side of 

 the stem, there are as a rule three, more rarely four hydrothecse, the lowest in the branch corner. 

 The hydrothecse are large, tubular, the free distal part of the adcauline wall amounts to about half 

 the length of the hydrotheca, and is somewhat more than the diameter of the opening. The hydro- 

 theca is bent to an angle, so that its free part forms an angle of about 60° with the branch axis. The 

 hydrotheca opening is nearly perpendicular to the branch axis; its margin has an adcauline sinus, in 

 which the large opercular plate is fastened. 



The gonothecse are situate on the upper side of the branches, and proceed from close under 

 the base of the hydrothecse. The male gonothecse are oval to pear-shaped, with six faint longitudinal 

 ribs terminating distally in as many blunt points; the aperture is centrally placed on a broad distal 

 cone. The female gonothecse are oblong pear-shaped, and have likewise six faint longitudinal ribs, 

 each with one or two markedly prominent spines on the distal part; the gonothecse lack distal 

 brood-chamber. 



Material: 



"Ingolf St. 96, 65°24' N., 29°oo' W., depth 735 fathoms, 1,2° 



- 98, 6 5 ° 3 8' N, 26 2 7 ' W, - 138 - 5,9° 



- 115, 70°5o' N„ 8°29' W., - 86 o,i° 



- 127, 66° 33 ' N., 2o J o 5 ' W., - 44 5,6° 



Diphasia attenuata belongs to the littoral region of the warm Atlantic, and penetrates at times 

 even far down into the abyssal region; the species has previously been quite frequently observed in 

 British waters. The finds at the threshold of Danmark Strait are therefore not surprising, but that 

 from Jan Mayen is remarkable, and must doubtless be accounted for as due to larval transportation, 

 possibly from the waters about Danmark Strait in the same way as the occurrence at the "Ingolf" 

 St. 127 at the north side of Iceland. 



The Ingolf- Expedition. V. 7. 15 



