HYDROIDA II 



125 



"Thor" 64°02' N., 22°33' W., depth 34 metres | labelled Sertularia leuera] 



63°30' N., 20°i4' W., — 80 — 

 Iceland: Bakkefjord, — 25—32 fathoms [labelled Sertularia tenera] 



Faskrudsfjord, — 20 — 50 — 



Vestmano — 25 — 



Hvalfjord, — 22 [some of the specimens labelled Sertularia 



tenera] 

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

 7 — N. by E. of Myggenses point, — 54 — 

 Vestmanhavn (depth not stated) 



Glyversnaes nearThorshavn ( — - — ) 

 Deep hole at north point of Nolso, depth 100 fathoms 

 5 miles S.S.E. of Bispen, — 50 — 



North Sea: 3V2 miles W. r / 4 S. of Ksergaarde beacon, 15 metres 



2 — N. by W. of Vederso beacon, — 18 — 20 — 



East coast of Southern Jutland (without further details). 



The study of the present extensive material of Sertularia cupressina has shown that variations 

 have played a predominant part in the separation of Sertularia species. Hi neks, in his classic work 

 on the British Hydroids (1868 p. 271) draws distinction between Sertularia argentea and Sertularia cu- 

 pressina on the lines that the former has a more bushy appearance, the latter a more "spire-like 

 apex", while at the same time the dark stem of the latter species contrasts strongly against the lighter 

 branches. In a large material, however, both these characters are seen to be subject to great variation, 

 and in both respects the two species pass gradually over one into the other. The other distinctive 

 feature is the hydrothecse, which are thus described: "The hydrothecse of the cupressina are appressed, 

 tubular, not much narrowed or divergent above, with a bilabiate mouth, while those of argentea are 

 shorter, swollen below, tapering upwards, with the aperture bent, sharply pointed at one side, and 

 oblique". We need not here dwell on the general form; this is, as will be seen from the figures here 

 given (fig. LXV) highly variable in one and the same branch. More weight should be attached to 

 the fact that the opening in Sertularia argentea is oblique, i. e. furnished with one more and one less 

 prominent tooth. Bonne vie (1899 p. 83) also, in her determinative key, attaches principal importance 

 to this feature, whereas Nutting (1904 p. 62) less happily lays stress upon the remaining features 

 in the hvdrotheca. Further investigation, however, soon leads to the conviction that the character is 

 based upon insufficiently careful study. Owing to the strong tendency of the species towards uni- 

 lateral hydrotheca arrangement on the upper branches, the hvdrotheca? will here be viewed in 

 oblique projection (cf. fig. LXV). Consequently, the outer tooth is seen in its full length, the inner 

 foreshortened in perspective. This is the cause of the oft-mentioned "asymmetry", which must conse- 

 quently be abandoned as a purely fictitious character. 



Both the mentioned species are noted in the literature as having the gonothecse furnished 

 distally with two lateral points, proceeding as outgrowths from the narrow margins of the gonotheca, 



