68 A. OKA. 



the muscles lying directly uiidenieath. The oral surface, on the other 

 hand, presents two longitudinal ridges extending nearly to the tip, and 

 separated from each other by a comparatively deep furrow, so that the 

 cross section of an arm has the outline of the letter B lying flat as 

 represented in fig. 7. 



Near the centre of the cross, each of the ridges just mentioned is 

 found to be continuous with its fellow of the adjoining arm, in such a 

 way as to form a right angle at the point of junction. In other words, 

 there are on the whole four L-shaped ridges on the oral surface of the 

 cross. 



As already mentioned, each aim is divided at the tip into two 

 branches, whose distal margin is furnished with a tuft of tentacular 

 process. These processes, which serve, no doubt, as organs of suction in 

 the act of procuring food, number, in this specimen 24 in a tuft ; there 

 being eight such tufts in all, the total number of tentacles possessed by 

 this medusa amounting to about 192. 



The calyx measures, when laid flat, 29 mm. in diameter, each arm 

 being about 11 mm. long and 3 mm. broad. The portion where the 

 arm is divided into two branches measures about 3.5 mm. 



This unique specimen, which was attached to a leaf of Zosfera 

 marina, was in fresh condition, of a dark green color exactly like that of 

 the latter. Owing to this close resemblance in color, it was detected 

 only with great difficulty, which doubtless explains the reason why it 

 has hitherto escaped our attention. 



Anatomy. In fig. 2 I have endeavored to show somewhat diagram- 

 matically the internal struture of the calyx of this medusa. The 

 coelenteric cavity (c), which is continuous throughout, extends to the tip 

 of the arms. In each arm there is a longitudinal septum (.9) which 

 divides the cavity into two lateral halves. The separation, however, is 

 not complete, for at the base of the branched portion there is an opening 

 (0) in the septum by which the cavities on both sides of it are brought 

 into communication with each other. 



The genital glands {g) form four "bands of irregular outline, each 



