(fraserI HYDROIDS OF THE VANCOUVER ISLAND REGION 151 



Obelia dichototna (Linnœus) 



PI. XV, Fig. 50 



Sertularia dichototna Linn^us, Syst. Nat., 1758, p. 812. 

 Obélia dichototna Fraser, West Coast Hydroids, 1911, p. 38. 



Trophosome. — Stem slender, erect, seldom more than 25 mm. 

 high, sometimes without branches but usually with branches irregu- 

 larly given off and these may be as long as the main stem so that they 

 have a dichotomous appearance; 3-4 annulations on stem and 

 branches above the nodes; pedicels rather short, given off in regular 

 alternation, usually annulated throughout; hydrotheca funnel- 

 shaped with polyhedral margin. 



Gonosome. — Gonangia borne in the axils on short annulated 

 pedicels, obovate, smooth, with a distinct collar which tapers from 

 base to margin; aperture rather small. 



Distribution. — Bremerton (Calkins); Departure Bay, San Juan 

 Archipelago (Fraser); Alert Bay, off Protection I., off Matia 1., 

 off Waldron I. 



Obelia dubia Nutting 

 PI. XVI, Fig. 51 



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

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



Trophosome. — Colony small, reaching a height of 25 mm., slightly 

 and irregularly branched, extensively annulated; pedicels usually 

 rather long and annulated throughout; hydrotheca large with broad, 

 shallow, rounded teeth ; vertical lines pass downward from the margin 

 for some distance from the indentations. 



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

 pear-shaped, with a distinct but low collar and small aperture; surface 

 almost smooth or provided with broad shallow corrugations. 



Distribution. — Departure Bay, Dodds Narrows, Ucluelet, San 

 Juan Archipelago, Queen Charlotte Is. (Fraser); Neck Pt., Five 

 Finger Islands, Snake I., Northumberland Channel, Cabriola Pass, 

 Friday Harbor. 



This species was always found in shallow water. In its early 

 stages it looks very much like the early stages of Obelia longissima 

 so much so that I find it impossible to distinguish between them at 

 times but in the mature state there is not so much resemblance between 

 thé short, annulated stems of 0. dubia and the long much branched 

 colonies of 0. lonvissima. 



