Dr. Du Plessis on a new PalaJicolous Medusa. 38o 
XLIII .—Ri searches on Cosmetira sal inarum, a new Palu- 
dicolous Medusa of the Environs of Cette. By Dr. Du 
PLESS IS *. 
The Medusae are almost exclusively pelagic zoophytes, inha¬ 
biting the open sea. They form a great part of the trans¬ 
parent and gelatinous animals that we meet with floating at 
the surface or at various depths under water. 
These creatures dread nothing more than fresh water, 
which is a destructive poison to them. Even brackish water, 
that of the sea mingled with more or less fresh water, kills 
them instantaneously. Moreover they constantly need a 
water rich in oxygen, fresh and incessantly renewed by the 
perpetual movement of the waves and currents. The Medusa?, 
in fact, have an almost equal dread of fresh water, of stagnant 
sea-water, and of a slightly too high temperature. All these 
considerations will enable the reader to understand how we 
were surprised, at the end of the month of June 1876, at 
finding, in the middle of the discharging-canal of the salt¬ 
works of Villeroy, near Cette, a charming Medusa, of a new 
species, which inhabits these salt marshes in the summer. 
It belongs to the genus Cosmetira , a section of the nume¬ 
rous group of the Oceanidse; and it is curious that it is a 
miniature copy of a much larger species, Cosmetira punctata , 
which occurs frequently in the sea near Cette, and at Nice, 
Naples, and elsewhere. 
All the interest possessed by this pretty little Medusa is con¬ 
centrated around the novel conditions to which this frail and 
charming creature must have accommodated itself in order to 
be able to exist in the localities tvhere we now meet with it. 
The canal, which serves for the discharge of the salt works of 
Villeroy, is a narrow trench, not more than 2 or J metres 
broad, and never exceeding 1 metre in depth. The soil is 
formed throughout of a black putrid mud, stinking of sul¬ 
phuretted hydrogen. The water is perfectly stagnant, for 
this canal, which is several leagues in length and surrounds 
all the salt-pans like an immense oval, is almost completely 
horizontal. Except for the imperceptible currents caused by 
the strong winds which sometimes blow over the pool of 
Thau (into which this canal opens by several passages), the 
water is therefore most frequently quite immovable. It 
is a true marsh-ditch, such as may be seen in the canals of 
the plain of the Orbe, canals which in all points resemble 
* Translated by \V. S. Dallas, F.L.S., from the ‘ Bulletin de la Society 
Vaudoise des Sciences NaturelleR,’ s^r. 2, vol. xvi. p. 39 (1879). 
Ann. <b Mag. N. Hist. Ser. 5. lb/, iii. 27 
