136 



HYDROIDA II 



"Thor" 64°02' N., 22°33' W., depth 34 metres 



— 63°3o' N., 20°i4' W., — 80 — 



- 6i°o7' N, 9°3o' W., - 835 - 

 Iceland: Reydarfjord, depth 45—80 fathoms 



Mouth of Berufjord, — 41—54 — 



Vestmano, — 25 — 30 — 



Hvalfjord, — 22 — 



Bredebugt, 64°45,8' N., 23°55,2' W. depth 30 fathoms 



Stykkishohn, — 3° — 



6 miles W. of Iceland, 65°32' N., 24°38' W., depth 22 fathoms 



Talknafjord, depth 22 fathoms 



Dyrafjord, — 15 — 



Onundarfjord — 10 — 



Adalvik (depth not stated). 

 The Faroe Islands: 6 miles N. by W. of Store Kalso, depth 60 fathoms 

 7 — N. by E. of Myggenses point, — 57 — 

 1-2 — N.W. of Agraleide, — 150 — 



Deep hole at north point of Nolso, — 100 — 



Stemnndsson (191 1 p. 92) briefly mentions that the branches in young colonies of Hydrall- 

 maiiia /alalia are at times short, unbranched, and biserial, and that the same is often the case with 

 the basal branches in somewhat larger colonies. Levin sen also (1913 p. 308) mentions small pinnate 

 colonies of 29 mm length from Hellebsek, Denmark, but without quoting further details as to the 

 hydrothectc. The frequent occurrence of the species in the Trondhjem Pjord has afforded an opport- 

 unity for closer study; the colonies are often very finely built. 



Young colonies of Hydrallnnuiia falcata may at times even at a length of 5 cm be singly pin- 

 nately branched, and it is then extremely difficult to distinguish them from Scrtularia. The stem, 

 which is here, of course, not yet spiral, has a hydrotheca at the base of each branch, a feature which 

 is likewise common in larger colonies from the Trondhjem Fjord, and which I have found in most 

 of the other colonies investigated from our seas. The hydrothecte on the branches in young colonies, 

 as also those on the branches in the pinnate basal parts of older ones, are arranged in two opposite 

 rows (fig. LXXIII) in such a manner that the symmetrical plane of the hydrothecse coincides with the 

 vertically set broad plane of the branches; the hydrothecte on these branches are alternately set, and 

 with ([uile a considerable interval between. The distal half, or more, of the adcauline wall is free; 

 llic length of the free portion is from once to twice the diameter of the opening. Quite young colonies 

 are thus extremely liable to be confused with small Serfiilaria colonies, unless the hydrothecte are 

 very carefull)- examined. The adcauline sinus in 1-Jydrallviaiiia is normally deeper than the abcanline; 

 the difference is, however, at times very slight, and if the closing membranes have fallen away, it is 

 very difficult to identify the colonics. 



When the colonies are somewhat larger, the spiral coiling of the stem begins to make its 



