[fraser] HYDROIDS OF THE VANCOUVER ISLAND REGION 195 



Trophosome. — Colony small ; stems often in dense masses growing 

 from stolons that are attached to eel-grass, slender, unbranched or 

 with few small branches; hydrothecae strictly opposite, each pair 

 unless two or three near the base, adnate on one side of the stem but 

 some distance apart on the other; they are tubular but somewhat 

 curved and directed well outward, about one-third free; margin with 

 two strong teeth, one of which is usually longer than the other. 



Gonosome. — Gonangia borne on the lower portion of the stem 

 just below the hydrothecae; they are large, oval, somewhat compressed, 

 with a short but distinct collar and large aperture; pedicel short and 

 curved; surface smooth or very slightly wrinkled. 



Distribution. — Ucluelet (Fraser) ; Clayuquot Sound, Pt. Grenville, 



Genus THUIARIA 



Trophosome. — Hydrothecae in two rows on stem and branches; 

 not in opposite pairs; hydrothecae with not more than two teeth, 

 operculum of one abcauline flap or two flaps (T. thuiarioides has an 

 operculum of one adcauline flap.) 



Gonosome. — Gonangia smooth or with two spines on the shoulders. 



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



A. Branches only on two sides of the stem 



a. Hydrothecae strictly alternate 



1 . Hydrothecae close T. alba 



2 . Hydrothecae distant T. distans 



b. Hydrothecae nearly opposite 



1. Branches in the same plane as the stem T. similis 



2. Branches twisted at the base into a plane at right angles 



to the stem T. dalli 



B. Branches on all sides of the stem 



a. Distal branches forming a dense tuft 



1 . Hydrothecae nearly opposite T. fabricii 



2. Hydrothecae strictly alternate. . 



i. Branches stiff; hydrothecae almost wholly immersed 



. . . T. thuja 



ii. Branches not stiff 



a. Operculum of one abcauline flap or two 



flaps T. robusta 



aa. Operculum of one adcauline flap 



T. thuiarioides 



b. Branches on the distal portion of the stem loosely arranged 



1 . Hydrothecae more than half free T. tenera 



2. Hydrothecae less than half free T. argentea 



Sec. IV, 1914—14 



