I24 HYDROIDA II 



gonothecse at the same time. This character should therefore be used with caution. In species where 

 the gonothecse are furnished with spines, the development of the spines themselves often varies greatly 

 in o-onotheca; which are fully developed and bear acrocysts; their number also is subject to accidental 

 variation in a striking degree. All this calls for discretion in using the gonothecse as specific 

 characters. 



The variational phenomena here mentioned show, that careful and critical judgement is necess- 

 ary in defining Sertularia species, at the same time indicating that many of the species already estab- 

 lished have little justification for their position as such. The present material does not include all 

 northern species, and cannot serve as a basis for thorough revision; it will nevertheless contribute to 

 the elucidation of certain synonyms. 



Sertularia cupressina Linne. 

 1758 Sertularia cupressina, Linne, Systema naturae, Ed. 10, p. 808. 

 1758 Sertularia argentea, Linne, Systema naturse, Ed. 10, p. 809. 



Upright colonies, the young ones, and the basal parts of the larger ones, to a greater or lesser extent 

 pinnate, with alternating or partly opposite branches. The older colonies have, for a shorter or greater 

 distal part, sinistrorse spirally coiled stem, so that the branches stand in a spiral. The stem is as a rule 

 distinctly prominent, monosiphonic, with a branch arising basally from the internodium; more rarely, 

 the latter may have two, or quite exceptionally three branches. The branches themselves are second- 

 arily more or less ramified dichotomically, their broad plane is in the pinnate parts perpendicular, in 

 the spiral horizontal. Between two successive branches on the same side of the stem or in the same 

 spiral there are two to four, as a rule three hydrothecse, the lowest at the branch angle. The branches 

 are divided up into irregular internodia with a varying number of hydrothecse on each; the hydrothecse 

 are on the lower branches oposite, or subalternately placed, and have a common plane of symmetry 

 with the branch ; on the upper branches they are more or less turned upward towards the upper side 

 of the branch; i.e. with a tendency to unilateral arrangement. The depth to which they are embedded 

 in the branch varies somewhat; the basal have a smaller, the distal a larger free distal part. The 

 adcauline wall has a free part from one-fourth to one-half the length of the hydrotheca; from one- 

 third to a little more than the diameter of the aperture. The hydrotheca has its greatest breadth 

 nearly at the middle, and narrows sharply towards the aperture, less markedly towards the base. The 

 opening has two strong lateral teeth of equal size. The abcauline opercular plate has a large free distal part. 



The gonothecse proceed from the branches close under the base of the hydrothecse, and on 

 the upper branches they are always on the upper side. They are pear-shaped to slender oval, and 

 oval in transverse section, distally provided with one or two lateral teeth in a highly variable stage 

 of development ; the teeth may also be entirely lacking. Distally, they narrow evenly down to a short 

 broad opening often surrounded by a short cylindrical neck. 



Material: 



"Thor" 65°52' N., 23°58' W., depth 62 metres 

 65W N, i3° 5 6, 5 'W, - 140 - 



