770 Proceedings of Royal Society of Edinburgh. [sess. 
upon the radial canals, a little more than half way between the 
stomach and the circular canals, and are nearer to the margin of 
the umbrella than to the stomach. Tentacles sixty to eighty-four. 
Their basal bulbs are very small, and some contain yellowish-brown 
or brown pigment. The amount of pigment is very small and is 
not visible to the naked eye. The root of the tentacle, within the 
margin of the umbrella, is semi-globular or oblong, and is usually 
without a transverse septum, but occasionally has one. Eight 
adradial marginal sense-organs, with a single otolith, situated on 
the inner side of the basal bulbs. 
Colour. — Gonads and stomach yellowish-brown or brown. 
Size. — Umbrella up to 2*5 mm. diameter. 
The medusa Obelia lucifera has not yet been traced to its 
hydroid. Obelia nigra can at once be distinguished by the black 
or very dark brown pigment in some of the basal bulbs. What I 
have called Obdia lucifera no doubt includes Obelia dichotoma, 
and very likely another species (but not Obelia nigra). I have 
twice failed to rear the medusa of Obelia geniculata , and the 
failures were probably due to my not succeeding in finding out 
the proper food for the young medusae. Until all the British 
species of Obelia have been reared from their respective hydroids, 
I do not think that I can determine the adult medusae with 
certainty. 
Obelia lucifera (Forbes).. (Tables I. 17 ; II. 22.) 
Thaumantias lucifera , Forbes, 1848, p. 52, pi. x. 
In 1901, it was only taken between 26th June and 22nd July, 
and was fairly common on the later date. 
In 1902, it appeared on 30th September and disappeared on 
15th November. Very scarce during October. 
Obelia nigra, Browne. (Tables I. 2; II. 5.) 
Obelia nigra , Browne, 1900, p. 721. 
In 1901, it appeared at the beginning of April and disappeared 
at the beginning of October. It was abundant off Little Cumhrae 
on 6th June. 
In 1902, it was taken from the middle of March up to the 
