ON THE VARIATION OF HALICLYSTUS OCTORADIATUS. 5 
group is larger than the others, and has two genital bands 
running towards it. This large group is perradial, and repre- 
sents the union of two adjacent adradial groups. Two other 
specimens show a similar variation. A slight alteration in this 
arrangement may take place by the union of two adjacent 
genital bands into one broad band (fig. 18). The genital bands 
usually start some distance down the body of the medusa and 
extend across the umbrella. Two specimens show an exception 
by having short bands commencing near the margin of the 
umbrella (figs. 19 and 20). 
The Variation in the Position of the Groups of Ten- 
tacles.—In most cases the change in position of the groups 
of tentacles is due to a decrease in number, and usually 
affects the symmetry of the umbrella. The decrease is some- 
times brought about by the union of two adjacent adradial 
groups of tentacles into an interradial (fig. 9) or a perradial 
group (figs. 6 and 18). 
In a few cases the position occupied by a group is excep- 
tionally abnormal. Two specimens have a group of tentacles 
on the oral side of the umbrella, some distance from the 
margin. One of these (figs. 7 and 8) has seven normal groups 
of tentacles, but the eighth group is a little way inside the 
margin, which projects beyond the group and has a tentacle- 
like colleto-cystophor in the position which 1s under normal 
conditions occupied by the eighth group of tentacles. The 
other specimen (figs. 12 and 15) has three septa, six colleto- 
cystophors, and five normal groups of tentacles. But there is 
also an abnormal group of tentacles upon a short stalk, which 
rises above the oral surface of the umbrella, and occupies a 
position about half-way between the centre and the margin of 
umbrella. Opposite this group of tentacles, upon the margin 
of the umbrella, there are two other sets of tentacles, close 
together, with the tentacles arranged in nearly a single row. 
An unique case amongst the abnormal forms is that of a 
specimen (figs. 1] and 13) with eight groups of tentacles and 
colleto-cystophors in the normal position. One of these gronps 
of tentacles is smaller than the others, and has, on its outer 
