marine British Shells and Animals. 201 
3 
. MEDUSA POCILLUM. 
Tas. XIV. Fig. 4. 
Body campanulate, furnished on the top with a sub-ovate, flat, 
and extremely thin striated crest or sail. The cup is whitisb, 
with a broad striated border of purplish-brown, margined with 
bright blue; the edges crenulated : within the cup are about ten 
larger sub-clavated tentacula, and many intermediate smaller | 
ones of a fine dark blue colour, which surround a central aperture. 
Length, including the crest, about three lines. Coast of De- 
vonshire. | | 
This exquisitely beautiful little animal was discovered on a 
piece of Spongia, where it attracted the eye by its brilliant co- 
lour. When placed under a microscope in sea water, it was 
observed to float on the surface reclining, so that the crest was 
never erect above the water; but it was doubtless in a relaxed 
state, having been carried some distance for examination. 
Whether the flat appendage in such a small Medusa can be of 
any use as a sail, to give it progressive motion by means of the 
wind, is very doubtful; but, like the dorsal fin of a fish, it must 
be most essential to keep it upright in the water. It evidently 
moved the crest or fin as well as the tentacula, and by their 
joint efforts obtained a slow: progressive motion. The longer 
tentacula were seen to move to and from the central mouth. 
To this crested or finned division of Medusa belong the Me- 
dusa Velella and the Holothuria spirans of Gmelin ; the former of 
‘which is the Velelle tentaculée of Bosc, figured in Histoire Naturelle 
des Vers, tom. ii. But those who wish to make a comparison 
we refer to the coloured figures of these two species in vol. vii. 
Nat. Miscel. tab. 247 and 250. Both these Meduse are ovate in 
the cup, and not orbicular as in the present species. 
| VERMES 
