310 ERNEST WARREN. 



Gonosome. — Male gonaiigium suhglobular, smootli, Avitli 

 flat operculum. Blastostyle may develop two gonopliores. 



Length, including stalk, about 0"84 mm. ; breadth 0"67 mm. 

 Operculum 0*21 mm. in diameter. The perisarc has a thick- 

 ness of 21 lit . 



(19) Sertularia bidens Bale. 



Sertularia bidens Bale. ' Oat. of the Australian Hydroid Zoophytes,' 



1884, p. 70. 



The Natal hydroid does not entirely agree with Bale's 

 description of bidens; but the dilferences appear to be 

 scarcely sufficient to warrant the formation of a new species. 

 The colour is a very pale brown, not dark brown, and the 

 height of the largest specimen found was only about 3 in. 



Trophosome. — Hydrorhiza forms a loose feltwork. Dia- 

 meter 0'172 mm., thickness of perisarc 22 ju. 



Hydrocaulu s. — Main stem bears pinnate stems irregularly 

 placed (text-fig. 10, A). Just below the first pinna of the 

 ])innate stem there is a conspicuous spiral groove running- 

 round the stem about twice {C). The portion of the stem 

 bearing pinna? is about half an inch in length. Pinna3 

 alternate. The stem is zig-zag, but the nodes are indis- 

 tinguishable; between two pinnte of one side there are three 

 hydrotheciu, one in the axil and two above. On the pinna; 

 the nodes are few, the first internode carrying 4 or 5 pairs 

 of hydrothecas, while the remainder carry from 1 to 3. 



Diameter of a pinna, measured just below the base of a 

 hydrotheca and about at the middle of its length, 0"152 mm.; 

 thickness of perisarc, 5"1 fx. 



Hydrothec a. — Subalternat e, not in contact with each other, 

 tubular, upper side horizontal, with the inner margin of the 

 mouth rather widely separated from the hydrocaulus (text- 

 fig. 10, D). Mouth horizontal, the outer margin provided with 

 two pointed teeth {t.) ; on the inside of the inner margin there 

 are usually developed two distinct knobs of chitin [ad.Ji.), 

 and on the opposite side on the outer edge there are a similar 



