HYDROIDA II 



55 



distinguishing features wliich have hitherto been regarded as good specific characters in Phimulariida. 

 There are undoubtedly, among tlie numerous recorded species of Plitwiilaria, s\nonyras in abundance, 

 and the new species and varieties which are constauth- 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 (Pluniularia 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 pinuata 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, especialh' the upper lialf 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 hydrothecae unilaterally arranged, and partly or entirely fused with the branch. 

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

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



Plumularia setacea (Liune) Lamarck. 



1758 Scrtularia 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 apoph\se has a hydrocla- 

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

 theca and three sarcothecte, and ever>- other one or exceptionally two sarcothecK in the median 

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

 at the opening of the hydrotheca. The length of the hydrotheca varies between 1/2 and 'j^ the length 

 of the internodium. The h\-drotheca is fused throughout its whole length with the hydrocladnim. 



The gonothecce 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 '/z— ','3 the length of the internodium; the iuternodia com- 

 paratively coarsely built. 



