6 FOSSIL MEDUS 2. 
It may be urged that the plaster sets very quickly, and that sediment 
deposited in the sea would require so much time for its consolidation that 
an organism as delicate as a medusa would be decomposed and crushed. 
In this connection I wish to record an observation made at the inlet west 
of Noyes Point, Rhode Island, which indicates that sediments may consoli- 
date and harden very rapidly under favorable conditions. A deposit, formed 
of fine sand and silt, hardened to such an extent during the time that 
elapsed between its deposition by the outflowing tide and the return of the 
tide that it was broken up by the waves of the latter so as to form a bree- 
ciated layer, the fragments of which remained, often with sharp edges, after 
the ebb of the tide on the following morning. That sediments may set and 
harden quickly under water is known to those who have waded or dredged 
in shallow waters in protected bays and inlets. 
Mr. H. Archer notes, in the following words, the mode of occurrence of 
a species that is referred to Polyclonia frondosa by Prof. Alexander Agassiz: 
A few years ago I was quartered for some time at Port Royal, Jamaica, and in 
the channels between the mangroves I observed what I at first thought were Actinize 
of large size on the muddy bottom, in about 8 feet of water. They were very numer- 
ous. I stirred one up with the boat hook, and was surprised to find it was a medusa 
turned upside down. On being disturbed it lazily contracted its umbrella in the usual 
manner and settled down again in the mud as before. The species was about a foot 
in diameter of umbrella, and dirty white in color. I never saw them swimming in the 
mangrove creeks, though I was frequently out in a boat, and they were at all times 
common on the bottom, lying as described. Some time afterwards I saw what seemed 
to be the same species at St. Georges Bay, a small island about 10 miles from Belize, 
Honduras. It was lying in the same position on the mud amongst the mangroves, in 
about 4 feet of water. I poked several up with a stick, and they slowly swam for a 
short distance and again settled down on their umbrellas. I believe it to be really 
the habit of the species to lie on its back, as it were, and it is interesting to find 
another kind in the East acting similarly. Mangrove swamps are extensive in the 
vicinity of Singapore, but I have not noticed any medusz here in that position, pos- 
sibly because there is a considerable tide which leaves the mud bare at low water.! 
Professor Agassiz, in commenting on Mr. Archer’s note, said: 
The medusa mentioned by Mr. Archer in Nature, Vol. XXIV, p. 307, is undoubt- 
edly Polyclonia frondosa Ag., figured in the Contributions to the Natural History of 
the United States. This medusa was already known to Pallas, who described alco- 
holic specimens sent him from the West Indies by Drury. It is stated by Agassiz to 
be quite common along the Florida Keys. I have myself observed it in great abun- 
1 Nature, Vol. XXIV, 1881, p. 307. 
