[fraser] HYDROIDS OF THE VANCOUVER ISLAND REGION 201 



the genus Diphasia 3 -, but in other respects it is quite unlike a Diphasia. 

 It has no internal marsupium in the female gonangium but has a 

 typical Thuiaria gonangium. Its mode of growth and method of 

 branching, etc., are distinctly Thuiarian. While noting it as an 

 exception in respect to the operculum, therefore, I see no valid reason 

 for not retaining it in this genus. 



Thuiaria thuja (Linnaeus) 



PI. XXXIV, Fig. 129 



Set tularin thuja Linn^us, Syst. Nat., 1758, p. 809. 

 Thuiaria thuja Fraser, West Coast Hydroids, 1911, p. 78. 



Trophosome. — Main stem rigid, not very stout; branches from 

 all sides of the stem, proximal ones usually broken off, leaving a stum}); 

 all branches stiff, branching dichotomously several times, making a 

 dense tuft, often spoken as the "bottle brush"; hydrothecae alternate, 

 closely placed, almost wholly immersed, tubular; margin almost 

 vertical without teeth; operculum a single abcauline flap. 



Gonosome. — Gonangia in rows that may be crowded on the stem 

 and proximal portions of the branches, oval, with short collar and large 

 terminal aperture and a short distinct pedicel; surface without 

 annulations or spines. 



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

 Matia I., off Waldron I., Friday Harbor. 



Family Plumularidae 



IVo^/w-some.— Hydrothecae growing only on one side of the 

 branches (hydrocladia), sessile, more or less adnate, nematophores 

 always present. 



Gonosome. — Gonophores producing fixed sporosacs, which are 

 often protected by special modifications of the branches. 



Key to the genera of Plumularidae found in the Vancouver I. region. 



A. Statoplean forms, i.e., those with fixed nematophores that are 



usually monothalamic 



a. Gonangia protected by corbulae which are modified branches 

 or hydrocladia Aglaophenia 



b. Gonangia protected by branchlets that are appendages of 

 hydrocladia Cladocarpus 



B. Eleutheroplean forms, i.e., those with movable nematophores that 



are usually bithalamic 



'-Die llydroiden (1er Arktischen Meere, 1909, p. 224. 



