1904 - 5 .] Report on Medusae found in Firth of Clyde. 769 
from Port Erin, which I have lately found in my collection, with 
the figures of M. fulva , I find that they agree so closely that 
they must he the same species. I think now that the Norwegian 
specimen must he regarded as an intermediate stage in the growth 
of M. polydiademata. With regard to the Plymouth specimen, I 
am still uncertain, and should like to see another specimen from 
the English Channel before coming to a decision. 
The geographical distribution of M. polydiademata is at present 
restricted to certain localities, where its hydroid no doubt lives. 
Romanes first found it in the Cromarty Firth, and states that it 
was somewhat rare. I found it at Port Erin in the spring of 1893 
and 1894, and Chadwick recorded it for June and July in 1899. 
It has not yet been recorded for the west coast of Ireland. 
Obelia dichotoma (Linnaeus). 
Obelia dichotoma , Hincks, 1868, p. 156, pi. xxviii. fig. 1. 
On 17th September 1902, hydroid colonies of Obelia dichotoma 
were taken from the piles of Keppel pier and placed in a bell- 
jar for the purpose of rearing its medusa to the adult stage. As the 
colonies were loaded with gonophores containing medusa-buds, 
within three days the bell-jar became crowded with young medusae. 
About a hundred were transferred to another bell-jar in which was 
working the plunger apparatus. 
The young medusa on liberation from its hydroid has sixteen 
tentacles and eight sense-organs. It is quite colourless and is with- 
out gonads. 
On 26th September, I examined all the medusae in the bell-jar. 
The largest were about 2-2*25 mm. in diameter, and had sixty-four 
tentacles and ripe gonads. 
On 9th October, the largest specimen measured 2*5 in diameter 
and had eighty-four tentacles. A few specimens were kept in the 
bell-jar until 17th October, but they showed no further increase in 
the number of tentacles ; the gonads had decreased in size owing 
to the shedding of the ova. 
Description of the adult medusa reared in a bell-jar : — The 
umbrella is disc-shaped, being circular and almost flat. The 
stomach is very short and the mouth has four lips. Four radial 
canals. The gonads are very small, oval in shape, and are situated 
PROC. ROY. SOC. EDIN. — YOL. XXV. 49 
