150 THE ROYAL SOCIETY OF CANADA 



Genus OBELIA 



Trophosome. — Stem branched, simple or fascicled. 



Gonosome. — Reproduction by means of free medusae which are 

 flattened dorso-ventrally and when liberated possess more than eight 

 tentacles. Eight interradial lithocysts are present. 



Key to the species of Obelia found in the Vancouver I. region. 



A. Stem fascicled 



a. Stem erect, hydrotheca with entire margin O. plicata 



b. Stem clinging, hydrotheca with sinuous margin .... 0. fragilis 



c. Stem erect, teeth with two cusps . 0. multidentata 



B. Stem simple 



a. Colony large 



1. Hydrotheca margin entire 0. borealis 



2. Hydrotheca margin sinuous 0. longissima 



b. Colony small 



1. Very much branched 0. griffini 



2. Not very much branched 



i. Margin sinuous, hydrotheca with vertical lines. . . 



0. dubia 



ii. Margin polyhedral 0. dichotoma 



iii. Margin entire, stem unbranched or very slightly 



branched 0. gracilis 



iv. Margin entire, stem with branches alternately 

 arranged 0. surcularis 



Obelia borealis Nutting 



PI. XV, Fig. 49 



Obelia borealis Nutting, Harriman Hydroids, 1901, p. 174. 

 Obelia borealis Fraser, West Coast Hydroids, 1911, p. 38. 



Trophosome. — Colony very large (Nutting reports it up to 18 

 inches), stem long and slender; main branches long and spreading, 

 given off in pairs or singly, the stem often sinuous at the nodes; stem 

 and branches with 3 or 4 annulations above the nodes; pedicels 

 either short and entirely annulated or long and annulated only at 

 each end ; hydrotheca funnel-shaped ; margin entire. 



Gonosome. — Gonangia borne in the axils on annulated pedicels, 

 obovate, a collar present, aperture large; surface smooth or with a 

 slight tendency to corrugation. 



Distribution. — Ucluelet, San Juan Archipelago (Fraser); off 

 Massett, Naden Harbor, Bull Harbor. 



