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 structm'e, 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 : — 



Hyalonemadae. 



Social zoanthoid polypes, secreting a central siliceous in- 

 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 distinct 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 laminae of which they are formed, the inner laminae pro- 

 jecting beyond the others, and the outer being the shortest. 

 (Brandt, t. 2. f. 12, 13, 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 



* Tho fractured or imperfect ends, the concentric ridges and spines on 

 the surface, and the spicules being surrounded with corium at once 



