322 



months) added to the Lily-house and the water is run off every year. 

 Probably a few specimens were last year or the year before present in 

 the tank, and have only this year multiplied in sufficient abundance to 

 attract attention. Clearly this Medusa is a tropical species since it flou- 

 rishes in water of the high temperature of 90" F. 



I have observed the Medusa feeding on Daphnia which abounds 

 in the water with it. 



The present form will have to be placed in a new genus. I shall 

 not on the present occasion propose any name for this new genus. 



It presents the common characters of the Trachomedusae (as distin- 

 guished from the Narcomedusae) in having its genital sacs or gonads 

 placed in the course of the radial canals. It possesses the solid ten- 

 tacles \vith cartilaginoid axis, the centrapetal travelling of the ten- 

 tacles, the tentacle rivets (Mantelspangen), the thickened marginal ring 

 of threadcells at the edge of the disc (Nesselring), characteristic of 

 Tracheline Medusae. 



Amongst Trachomedusae the new form finds its place in the Peta- 

 sidae which are characterized as Trachomedusae with 4 radial canals, 

 in the course of which the 4 gonads lie, with a long tubular stomach 

 and no stomach-stalk. 



Amongst Petasidae it is remarkable for the great number of its 

 tentacles which are all solid, and for its very numerous otocysts. Further 

 it is remarkable among all Hydromedusae (Velate Medusae, that is ex- 

 clusive of Charybdea, for the fact tliat centrifugal radiating canals, which 

 are neither more nor less than the elongated otocysts, pass into the 

 velum where they end corcali y. 



The genus may be characterized as follows : 



Mouth quadrifid with 4 perradial lobes. 



Stomach long and tubular, projecting a good deal below the disc. 



Disc saucer shaped, that is flattened. 



Radial canals 4, opening by dilated ends into the marginal canal. 



Gonads 4, in the form of 4 oval sacs depending into the cavity of 

 the sub-umbrella from the 4 radiating canals. 



Marginal or ring Canal voluminous. 



Centripetal Canals (such as those of Olindias, Geryonia etc.) absent. 



Tentacles solid in three sets which are placed in three superimposed 

 horizons. 



1) a set nearest the aboral pole of 4 large per-radial tentacles. These 

 are the primary tentacles. 



2) a second tier of 28 (or more) mediumed sized tentacles placed 

 between these in four groups of seven. These are the secon- 

 dary tentacles. 



