56 



HYDROIDA II 



Forma microtheca: length of hydrotheca '/ 4 — I / s the length of the internodintn; the internodia 

 of slender build. 



Material (forma typica): 



"Thor" 35°57' N., 5°35' VV., depth 740 metres 

 Iceland: Vestmano, depth 50 fathoms. 



Plumularia setacea divides in the same manner as the foregoing into a widely distributed warm 

 water variety, forma microtheca, and a temperate forma typica, occurring both in subantarctic and boreal 

 waters. Plumularia setacea is in northern waters a denizen of the middle and upper parts of the lit- 



200 m. , boom. _ 1000 m. _. j ooo m. 



Fig. XXIV. The occurrence of Plumularia setacea in the Northern Atlantic. 

 In the hatched parts the occurrence according to the literature is common, although scattered. 



toral region, whereas in warmer seas it goes fairly deep down into the abyssal region. The species 

 is altogether somewhat rare in the boreal area (fig. XXIV) and penetrates in considerable numbers 

 only into the southern and warmest parts of the same. 



Plumularia Catharina Johnston. 

 1833 Plumularia Catliarina, Johnston, Illustrations in british Zoology, p. 497, figs. 61 — 62. 



Upright, pinnate colonies with simple or branched, monosiphonic, little pronounced stem. The 

 branches proceed from the base of the hydrothecse on the stem, and are as a rule placed oppositely, 

 more rarely alternating. Stem and hydrocladia are divided into internodia by alternating transverse 



