272 Dr. J. E. Gray on Hyalonemata. 
mud; and he said that the collector told him that they lived 
with part of the coil sunk in the mud. I did not credit the 
account then, but I see reason to do so now. 
I believe that it will be found that the coral grows erect, 
with the part of the coil not covered with animals sunk in the 
mud, like the Sea-pen or Pennatula (the siliceous spicules, 
not being liable to disintegrate or change in structure, are well 
adapted for such a mode of life in their uncovered state), and 
that the sponge when present is a parasite that grows at the 
apex, and not, as has hitherto been considered, at the base of 
the coil of the coral. 
If this theory is the true one, as I believe it to be, the family 
and genera may be thus characterized :— 
Hyalonemadz. 
Social zoanthoid polypes, secreting a central siliceous m- 
ternal axial coil for their support. The upper half of the coil 
covered by a uniform cylindrical bark regularly studded with 
retractile polypes. The polypes are developed at the apex and 
are directed upwards as the coral grows; those on the bark 
near the naked part of the spicules are degenerate or less 
developed than those on the other part of the bark; they ap- 
pear to die off below as the lower part of the coil sinks deeper 
in the sand. 
The axis consists of numerous siliceous threads or spicules 
extending from end to end and coiled together into a cylindri- 
cal rope-like form. 
The spicules, as far as they are covered with the bark-like 
polypes, are each surrounded and separated from each other by 
a thin sheath of corium, the whole forming a dense cylindrical 
coil enclosed by the external bark formed of the united polypes. 
The part not covered with the bark consists of the lower 
half of the same spicules, which are separate and distinet from 
each other, forming a beautiful tuft of glassy filaments. 
Each spicule is formed of a great number of concentric 
coats with a central canal, like the spicules of sponges; but 
the ends of the spicules are unfinished and truncate, showing 
the lamin of which they are formed, the inner lamine pro- 
jecting beyond the others, and the outer being the shortest. 
(Brandt, t. 2. f. 12, 18, 15; Schultze, t. 2. f. 3, 4, 5.) 
The spicules are linear-elongate, subcylindrical, unequally 
fusiform, tapering at each end, the end that is enclosed under 
the bark being the longest and most slender*. (Brandt, t. 2. 
f.12, 13, 14, 15.) The surface is smooth, but near each end 
* The fractured or imperfect ends, the concentric ridges and spines on 
the surface, and the spicules being surrounded with coriwm at once 
