128 HYDROIDA II 



The young colonies are always pinnate, the larger ones now pinnate, now with distally sinist- 

 rorse stem. The stem itself is but slightly pronounced, if at all; it is monosiphonic and indistinctly 

 segmented, with almost regularly alternating branches. The branches again produce irregular, not 

 infrequently alternating branchlets, which may further be tertially ramified. The pinnate portions of 

 the colonies have the broad plane of the branches perpendicularly set; in the spirally coiled ones, on 

 the other hand, it is horizontal. On the same side of the stem, or in the same spiral, there are three 



very rarely two or four hydrothecse between two successive branches, the lowest 

 in the branch corner. The branches are divided into irregular internodia with a 

 varying number of hydrothecse. The hydrothecse are subalternately to alternately 

 placed; their plane of symmetry coincides, in the pinnate portions, with the broad 

 plane of the branches, but is often much displaced in the spiral parts, so that 

 the hydrothecse here often come very near to unilateral arrangement on the 

 upper side of the branches. The hydrothecse are not very deeply imbedded, and 

 have a highly diverging distal part; the free distal part of the adcauline wall 

 is almost invariably more than half the length of the hydrotheca, and twice to 

 three times the opening diameter. The maximal breadth is near the middle 

 decreasing thence equally to either end. The aperture margin has two distinct 

 somewhat rounded lateral teeth of equal size; the abcauline large lid plate has 

 a large free distal part. 



Fig. LXVII. Sertularia te- 



nera. Part of a branch with a The gonothecse are attached to the branches close under the base of 



polygonal gonotheca from h h droth in the spiral part always on the upper side of the branch. The 



the Kara Sea, "Dijmphna ". ' 



(X 40). gonothecae are oval, and round or polygonal in section, in the latter case with 



four to six, most frequently five sides; they have distally a broad round opening and an often almost 

 imperceptible tubulous neck. 



Forma spitzbergensis: large, spiral and bushy colonies'with approach to unilateral arrangement 

 of the hydrothecae. 



Forma sibirica: large, pinnate, slender colonies with no indication of unilateral arrangement in 

 the hydrothecse. 

 Material : 



"Ingolf" St. 69 624o' N., 22 1 7' W., depth 589 fathoms 3,9 



"Thor" 64i6' N., 22i7' W., 50 metres 



Greenland : Egedesminde, on Boltenia, 30 50 fathoms 



Iceland: Hvalfjord, 22 



The Faroe Islands: 2 miles N.W. of Agraleide, depth 150 fathoms 



Kara-Sea: "Dijmphna" [labelled Sertularia argentea and Sertularia Dijmphnte]. 



Sertularia tenera stands clearly apart from the foregoing species, and appears to vary some- 

 what less in the shape of the hydrothecse. The two geographical varieties are peculiar; the only real 

 distinction lies in the habitus of the colony, and it is not altogether rare to find transition forms, 

 especially in the Murman Sea. We are still, however, unaware as to what factors exert the determin- 

 ative influence upon the shape of the colonies. 



