918 ADDENDA TO THE AUSTRALIAN HYDKOMEDUSJE, 



four Radical Canals meet. No elongated Manubrium. Mouth 

 narrow. Mouth styles touching at the base. The Gonads do not 

 extend to the Radial Canals. The Polypcolonies are branched ; 

 the alimentary Po]yps possess one vertical of filiform tentacles, 

 the Medusae, bud on peduncles, which arise out of the Hydrorhiza. 



185a (237.) MARGELIS TRINEMA. Nov. spec. 



Plate XLL, Fig. 13. 



Umbrella semi-spherical, a trifle higher than broad. Stomach 

 short, cylindrical, nearly half as long as the Umbrella ; not quite so 

 broad as long. Gonads in the shape of four pair of oblique folds. 

 The folds ascending towai'ds the primary Radii. Mouthstyles 

 about as long as the stomach, the margin of the mouth between 

 the styles straight. Each style bears at its end three small eqral 

 brandies, about a third as long as the style. These mouth-styles 

 are carried upward. 



The Tentacle-bulbs ai'e small, broader than high, and thick. 

 From each bulb three tentacles take their origin, which are about 

 half again as long as the Umbrella ; also the tentacles are curved 

 upwards terminally (Fig. 13.) 



Colour : Medusa colorless. Entoderm of stomach and tentacle 

 bulbs dark yellow. 



Size : Diameter of Umbrella, 2-3 mm. 



Ontogenesis : I have found some Bougainvillia's in Port Jackson, 

 which are similar to B. ramosa. They are the only Hydroid Polyps 

 resembling that Genus, which I have met with in Australian waters. 



It seems therefore not unlikely that they are different stages in 

 the cyclus of development of our Margelis trinema. Both how- 

 ever, Medusa and Polyp are rare, so that not much reliance can be 

 placed on that assumption. 



Locality : Port Jackson. 



Season : Early Spring. 



