604 THE AUSTRALIAN HYDROMEDUS^E. 



203. OBELIA AUSTRALIS. nov. sp. 



The Medusa is not known to me in the adult stage. At the 

 time of liberation it is similar to a newly-born Obelia geniculata 

 for instance. 



The Polype colony however, presents a few peculiarities by which 

 it diflers from other species of Obelia. The stem of this Obelia is 

 creeping, adnate to foreign bodies, to which it clings like a Hydror- 

 hiza. The stem bears Hydranths on very short annulated stalks, 

 and also a few very short branches with nearly sessile Hydrothecse. 

 These creeping stems are short, and take their origin from a distinct 

 Hydrorhiza, which differs from the creeping stem by the much 

 greater thickness of its Perisarc and by the numerous anostomoses 

 which cause it to attain a reteform appearance. The Gonophores 

 have the ordinary elongate shape. 



Colour : Perisarc of Hydrorhiza reddish brown. Perisarc of 

 stem and branches light orange. Entodermal Epithelium of Poly- 

 postyles, Medusa buds and the proximal part of the stomach of 

 the Hydranths brown. 



Size : Length of creeping stems 12-16 mm., erect branches, 

 3-4 mm. 



Ontogenesis unknown. 



Locality : East coast of .New Zealand, Sumner, Laminarion 

 zone. 



Season : Gonophores produce Medusae from May to July. 



50. GENUS TIAROPSIS. L. Agassiz. 



Eucopinse with eight adradial marginal vesicles and numerous 

 tentacles (16 or more up to 300). Eight marginal vesicles with 

 numerous Otolithes, always betioeen two tentacles. No marginal 

 cirrhi. Eour Gonads around the four Radial Canals, no stalk to 

 the stomach. Polyp colonies unknown. 



