

BY R. VON LENDENFELD, PH.D. 605 



204. TIAROPSIS MACLEAYI. nov. sp. 

 Plate XXIII., fig. 37. 



I have named this beautiful, but unfortunately rare Medusa 

 after the worthy patron of Zoology in the Australian Colonies. 

 The Umbrella is flat, corresponding to about the quarter of a 

 sphere, twice as broad as high. Stomach quadrangular, prismatic, 

 about -J as long as the Umbrella cavity, mouth with four very small 

 lips. Gonads along the upper two-thirds of the Radial Canals. 

 Tentacles about 100, short and slender, with small basal Ocellus, 

 which is however, perceptible only at the base of a few tentacles 

 and makes the impression of a rudimentary organ, Eight large 

 marginal vesicles. The structure of these vesicles differs in so far 

 from the ordinary auditory organs of the kind, as its inner wall is 

 produced into numerous folds between which the Otoliths lie. Polyp 

 colony unknown. 



Colour : Medusa light rose-coloured. Gonads dark red. Bulbs 

 at the base of the tentacles and Entoderm of the stomach brown. 

 Tentacles nearly colorless. 



Size : The largest adult specimen measurtd 12 mm. aci'oss, and 

 was 5 mm. high. 



Ontogenesis. The first stages at the development of the ovum 

 were traced, and it appears that the development of this Hydro- 

 medusa is most like that described by H. Fol (1) of Geryona. The 

 cells of the blastula, when 32 in number divide irregularly in a 

 similar way as in Geryonia (I.e.) A division between a clear 

 Entodermal, and an opaque Ectodermal portion does not take plac 

 in such a manner as in Geryonia. Ectoderm and Entoderm are 

 nearly alike as far as the contents of the cells are concerned ; they 

 differ only in shape. The cells of the delaminated Entoderm are 

 higher and altogether much bulkier than the colls of the Ectoderm. 

 All the Embryos died at a certain age, when they consisted of 

 about 200 cells, so that the further development could not be 

 traced. 



(1) H. Fol. Die erste Entwickelung des Geryouideneies, Jenaische Zeit- 

 schrift. Band VII. 

 40 



