NOTE ON THE OCCURRENCE OF CASSIOPEA XAMACHANA 
AND POLYCLONIA FRONDOSA AT THE TORTUGAS. 
(Plate 4, figs. 17-20.) 
Amongst the various forms of plants and animals which find a conven- 
ient and salubrious abode in the warm storm-proof waters of the Fort Jef- 
ferson moat, none is more characteristic than the rhizostomous scyphozoan 
medusa Cassiopea xamachana Bigelow. The favorable conditions which 
3igelow! found to prevail in the Salt Ponds of Jamaica must have been 
very much the same as those which are so marked in the sheltered moat 
in the Tortugas. 
Besides the large bronzy-black ascidians that grow upon the rock walls 
of the moat at tide-mark, no creature is so conspicuous to the eye of the 
zoologist as the feathery brown disks that fairly carpet the floor of this place. 
When the surface of the water is unruffled, these jelly-fishes can be 
counted by the hundred as they lie on the warm sand or amongst the masses 
of alge, the fluffy branches of the oral arms uppermost, the edge of the 
disk lazily fanning at the rate of a few strokes to the minute. “ Moss 
cakes ” the marines at the fort called the great creatures. Judging by both 
size and numbers, this species has here found an ideal breeding-ground.? 
The medusz vary in size through a wide range, and the extremes are as 
apt as not to be found resting side by side on the sand. 
The largest examples measured 145 to 155 mm. in diameter, and there 
were very many of this size. The smallest specimens were less than 25 
mm. in diameter, and they were characterized by less distinct markings, 
oral arms of smaller proportionate size, and greater activity of habit. The 
parts of the moat where the bottom was composed of clean sand, with only 
a fathom of water, seemed most favorable to the small individuals. In 
these younger cassiopeas the number of marginal sense-organs was from 
13 to 15, while the largest and oldest ones possessed from 18 to 22. 
Sexual multiplication.—Very little is known about the reproductive pro- 
cesses of the rhizostome meduse. Bigelow, in his admirable monograph 
on this species, has given us a most entertaining as well as thorough account 
* Bigelow, R. P. 1900. Memoirs Boston Soc. Nat. Hist., vol. 5, No. 6. Anatomy 
and development of Cassiopea xamachana. 
* The first record of the occurrence of this species in this locality is given by 
Fewkes, J. Walter, 1882: Notes on Acalephs from the Tortugas (Bull. Mus. Comp. 
Zool. 1x, 7). While his determination of the specimens found at Fort Jefferson was 
as Cassiopea frondosa, his description and figures, and the occurrence of C. ramachana 
in the same locality, make it clear that Bigelow was justified in assuming that the 
species was in fact C. xamachana. 
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