upon Luminous Animals. 267 
three quarters of an inch in diameter. The margin of the 
umbella was undivided, and surrounded internally by a row 
of pale brown spots, and numerous small twisted tentacula : 
four opaque lines crossed in an arched manner from the cir- 
cumference, towards the center of the animal : an opaque 
irregular shaped process hung down from the middle of the 
umbella : when this part was examined with a lens of high 
powers, I discovered that it was inclosed in a sheath in which 
it moved, and that the extremity of the process was divided 
into four tentacula, covered with little cups or suckers, like 
those on the tentacula of the cuttle fish. 
This species of medusa bears a striking resemblance to the 
figures of the medusa hemispherica, published by Gronovius 
and Muller ; indeed it differs as little from these figures, as 
they do from each other. Its luminous property, however, 
was not observed by these naturalists, which is the more 
extraordinary, as Muller examined it at night, and says it is 
so transparent, that it can only be seen with the light of a 
lamp. If it should be still considered as a distinct species, or 
as a variety of the hemispherica, I would propose to call it 
the medusa lucida, 
In this species, the central part and the spot round the 
margin, are commonly seen to shine on lifting the animal 
out of the water into the air, presenting the appearance of an 
illuminated wheel, and when it is exposed to the usual per- 
cussion of the water, the transparent parts of its body are 
alone luminous. 
In the month of September 1805, I again visited Herne 
Bay, and frequently had opportunities of witnessing the 
luminous appearance of the sea. I caught many of the hemi- 
