138 Papers from the Marine Biological Laboratory at Tortugas. 
the lower tentacles, and the location of the gonophores considerably above 
the latter, are points distinguishing the species from those described by other 
observers. 
No specimens appeared in which there was any sign of a branching colo- 
nial stock, such as is described as an occasional form of the trophosome of 
C. allmant! and C. dujardinu.? 
Habitat—Not found thus far in any other locality than that given above 
for the medusa form, viz, the growing filamentous alga, abundant in the 
Fort Jefferson moat. Owing to its small bulk and unobtrusive appear- 
ance, it would be difficult to discover this hydroid upon any other than a 
very delicate foundation. It may be abundant upon stones and shells, etc., 
in the bottom of the moat, but it would be only by rearing the medusz in 
aquaria containing nothing else that one would be likely to find it there. 
III. GENERAL ACCOUNT OF THE MEDUSA STAGE OF CLADONEMA MAYERI. 
The occurrence in the moat at Fort Jefferson of this species of Clado- 
nema, or of any species of the genus for that matter, is certainly surprising. 
It would be difficult to find a part of the ocean more unlike the habitation 
one would select as that for which the structure of this creature seems to 
fit it. Here is a creature very unusually equipped for life in the open sea, 
capable of resisting ocean-currents, tides, and boisterous waves, provided 
with ballast and a whole battery of anchors against the assaults of tempests. 
It has established itself in cowardly fashion within the sheltering walls of a 
placid ditch, well out of harm’s way. 
The moat at Fort Jefferson, surrounding the hexagonal fortifications, is a 
relic of the ancient days of short-range artillery. It was constructed by 
throwing a substantial wall of masonry around the vertical face of the fort, 
founding it upon the natural bottom of coral rock. The moderate tides have 
access through the generous sluiceways, built large enough to permit the 
passage of small boats. Although shallow, the moat is never empty, nor is 
its bottom, which rises to within a few feet of the surface at low water, 
ever entirely uncovered, even in the shallowest parts. The water is warmed 
by the sun and by reflected heat from the shallow, sandy bottom and the 
brick walls of the fort. The temperature of the water is often high enough 
to make it feel decidedly warm to the hand when the air is well up in the 
eighties, Fahrenheit. 
The ecology of the moat offers a most interesting problem. A number 
of species have become established here which never make their appearance 
in the waters outside the wall of the moat. The warmth and quietness of the 
water is partly the cause of this condition, but there is also to be taken into 
account the presence, because of that same warmth and protection from 
* Allman, J. G., 1871. Monograph of Gymnoblastic Hydroids. 
?Dujardin. Ann. des Sci. Nat., 1843, p. 370. 
