[fraser] HVDROIDS OF THE VANCOUVER ISLAND REGION 177 



divided by a deep constriction from the base of the hydrotheca; 

 on this shoulder there are two nematocysts present, which are deeply 

 cup-shaped and are supported by a two-ringed pedicel. The hydro- 

 thecae widen gradually and symetrically until the diaphragm is reached ; 

 from this point the under surface passes out almost in a straight line, 

 while the upper surface is convex for some distance, after which it 

 passes out parallel to the lower side; the margin is but slightly flaring, 

 it is commonly duplicated. 



Gonosome. — Unknown. 



Distribution. — San Juan Archipelago (Fraser). 



Family Sertularidae 



Trophosome. — Hydrothecae sessile, usually arranged on both 

 sides of the stem and branches, and more or less adnate to them. 



Gonosome. — Gonophores producing fixed sporosacs, never free 

 medusas. 



Key to the genera of the Sertularidae found in the V.I. region 



A. Hydrothecae all on one side of the branches, their distal ends 



alternating to right and left Hydrallmania 



B. Hydrothecae arranged in two longitudinal rows 



a. Hydrothecae in opposite pairs Sertularia 



b. Hydrothecae alternate 



1. Operculum of one adcauline flap 



i. Hydrothecal aperture small, body flask-shaped. . . 



A bietinaria 



ii. Hydrothecal aperture large, body not flask-shaped 

 Diphasia 



2. Operculum abcauline or with more than one flap 



i. Operculum of 3 or 4 pieces Sertularella 



ii. Operculum of 1 or 2 pieces Thuiaria 



C. Hydrothecae arranged on all sides of the branches 



a. Operculum usually of one flap Selaginopsis 



b. Operculum of several flaps Dictyodadium 



Genus ABIETINARIA 



Trophosome. — Hydrothecae alternate, flask-shaped; aperture 

 small; operculum with a single adcauline flap. 



Gonosome.- — Gonangia without spines or internal marsupium. 



Key to the species of Abietinaria in the Vancouver I. region 

 A. Stem stout 



a. Gonangia with strong longitudinal crests 



