1904 — 5 .] Report on Medusae found in Firtli of Clyde. 
759 
The stomach is cone-shaped. Four oral tentacles, which are two 
to three times dichotomously branched. Four radial canals. The 
gonads have not yet begun to develop. Four perradial marginal 
tentacles with large basal bulbs. Ocelli absent. 
Colour. — By transmitted light, stomach bright yellowish-brown. 
The lower half of the basal bulbs bright yellow, the upper half 
(embedded in the jelly of the umbrella margin) yellowish-brown. 
By reflected light, stomach and basal bulbs bright orange. 
Size, — Umbrella about 1*5 mm. in length. (This specimen was 
taken with its umbrella turned inside out.) 
The genus Thctmnitis was established by Haeckel (1879), and 
the type species is Thamnitis tetrella , Haeckel, which was found 
on the coast of Brazil. There is no figure published of the type 
species, and its description is rather brief. 
In this genus Haeckel has placed Bougainvillia nigritella, 
Forbes (1848). This species is not a Thamnitis , but belongs to 
the genus Margelis , and its hydroid is probably a Bougainvillia. 
The medusae, which belong to the genus Margelis , begin their 
free-swimming life on liberation from their hydroid, with four 
perradial groups of tentacles. In each group there are two 
tentacles, and a further increase in number takes place as the 
medusa grows larger and older. The basal bulb of a Margelis is a 
compound bulb, from which spring two or more tentacles. 
In the Millport Thamnitis there is only a single tentacle in each 
perradius, and it is situated in the centre of a large conspicuous 
bulb. 
All the British species of Margelis have coloured ocelli, which 
are situated either on the extreme margin of the compound bulb 
or on the base of a tentacle. The number of ocelli corresponds 
with the number of tentacles. The Millport T'hamnitis has not an 
ocellus (the specimens were examined alive). The presence of 
single perradial tentacles and the absence of ocelli indicate that 
it is not a young Margelis. Judging from the appearance of the 
basal bulbs, I do not think that any more tentacles are likely to 
develop. These specimens, in general appearance, are not like a 
young Margelis , so that I do not consider it to be a case of 
numerical variation. They are certainly early stages, and at 
present there is no clue to the adult form. Before describing these 
