HYDROIDA II 



55 



distinguishing features which have hitherto been regarded as good specific characters in Plumulariida. 

 There are undoubtedly, among the numerous recorded species of Plumularia, synonyms in abundance, 

 and the new species and varieties which are constantly being described do not make matters better. 

 New forms demand not only morphological but also other justification, as is the case with the forms 

 here noted. The variant group indicated as forma typica penetrates exceptionally (Plumularia Helleri) 

 right into the Mediterranean, but has otherwise its main distribution in the boreal waters and in sub- 

 antarctic regions, thus exhibiting a tendency to bipolar occurrence (cf. Broch 1914). Forma elegantula 

 on the other hand, which is remarkable for its fine slender build, predominates under tropical-subtro- 

 pical conditions, and is only on rare occasions met with in the temperate seas. 



The area of distribution for Kirchenpaueria pinnata forma typica in northern waters coincides 

 in the main with the fields on the chart (fig. XXIII); it is likely, however, that new finds will be 

 made off the coast of Iceland, and we must wait until the species has been further localised in Green- 

 land waters, before the query on the label can be erased. Kirchenpaueria pinnata appears in the 

 northern waters as less susceptible to diminished salinity, and thus penetrates far up into the fjords; lower 

 temperature, however, soon sets a limit to its progress. In the northern seas, it belongs to the littoral 

 region, especially the upper half of the same, and only exceptionally occurs down in the abyssal. 



Gen. Plumularia (Lamarck). 



Upright, single or double pinnate colonies, the stem bearing on its apophyses undivided bran- 

 ches (hydrocladia) with hydrothecse unilaterally arranged, and partly or entirely fused with the branch. 

 The apophyse lacks sessile large sarcothecse; the sarcostyles are situated in two-chambered mobile 

 sarcothecae, generally a pair at the mouth of each hydrotheca. 



Plumularia setacea (Linne) Lamarck. 

 1758 Sertularia setacea, Linne, Systema naturse, ed. 10, p. 813. 

 1816 Plumularia setacea, Lamarck, Histoire naturelle, vol. 2, p. 129. 



• Single pinnate colonies with monosiphonic main stem. The stem is divided into short inter- 

 nodia, each with a distal apophyse, turned alternately to either side. Each apophyse has a hydrocla- 

 dium divided by transverse joints into internodia, of which latter every alternate one bears a hydro- 

 theca and three sarcothecae, and every other one or exceptionally two sarcothecse in the median 

 line; the hydrotheca-bearing internodium has a proximal, median sarcotheca, and a supracalyciue pair 

 at the opening of the hydrotheca. The length of the hydrotheca varies between I / 2 and '/ 5 the length 

 of the internodium. The hydrotheca is fused throughout its whole length with the hydrocladium. 



The gonothecae arise from the branch apophyse on the stem. They are elongated oval, with 

 a cylindrical, narrow, often somewhat curved neck; the males are smaller than the females. The colon- 

 ies are as a rule hermaphroditic, with the male gonangia on the basal part. 



Forma typica: length of hydrotheca t / 2 — I / i the length of the internodium; the internodia com- 

 paratively coarsely built. 



