SOME MEDüS.T: of JAPANESE WATERS. 23 



Rhizostomae. 



Crambessidae. 

 TJiysanostoiiia thysanuvaf Hreckel. 



The umbrella is shallow, disc-shaped, four times as broad as 

 high. It is thick in the centre, but becomes suddenly thin at 

 the hanging marginal parts. The latter is curved axially, and 

 are divided into about 120 lobes. About 13 velar lobes are found 

 between every two narroAV ocular lobes. The exumbrella is finely 

 granulated, the granules being about 1 mm. in diameter. 



The oral pillars are very short and narrow, having very wide 

 subgenital ostia between them. They are about 2/7 as wide as the 

 diameter of o^ia. The oral disc is quadrate with much vaulted 

 aboral surface, on which I could not find the quadrate depression 

 figured and described by Hœckel. 



The oral arms are about twice as long as the umbrella-dia- 

 meter. They are nearly of the same breadth from root to tip. 



I have obtained a fine specimen of this species measuring 

 160 mm. in diameter, from the harbour of Tateyama. The 

 Zoological Institute of the Science College is in possession of two 

 smaller specimens collected by Mr. K. Aoki, off Atami in Prov. 

 Izu. They are 55 mm. and 60 mm. in diameter respectively. 



This species is quite different from the medusa which I had 

 described under the name of Tk. denscrispum, though Maas thinks 

 this to be a youug form of Hseckel's Th. thysanura. 



