252 DESCRIPTION OF CHALK CORALS. 
connected with the viscera, and which secreted a large proportion of animal 
matter among the calcareous particles ; whereas the solid enduring body of the 
coral was developed from others belonging to the mantle, and which deposited a 
preponderating amount of mineral ingredients. The irregularities within the ab- 
dominal cavities both large and small appeared, so far as was observed, to arise 
from the imbedded position of the hollows. The greatest inequalities existed in 
those specimens (fig. 16) which had immersed cavities, as if a struggle had been 
maintained at periods of increase, between the visceral and pallial portions of 
the polype ; and it should not be forgotten that one of the properties of the latter 
structure is to close over areas unoccupied by it; on the contrary, in specimens 
(fig. 14) characterized by cavities which possessed during growth a great degree 
of free surface, subsequently thickened, the interior was remarkably uniform in 
outline, and traversed only by faint vertical lines, or impressions derived from 
lamellae edges. 
In a summary of differences between Oculina and the chalk fossil, it would 
appear, (1) that in the latter, dominant cavities ranged upwards from the base 
to the full extent of the coral, no limits to their growth being evident, whereas 
in Oculina no similar hollows exist: (2) that the cavities produced at the upper 
extremity of the corals spring in Oculine from the investing portion of the polype, 
and contemporaneously around their area ; while in the chalk fossil the formation 
was effected progressively as the margin of the parent hollow was advanced : (3) 
that according to the authorities quoted in a preceding paragraph, only one or two 
germs spring in the recent genus from the upper end of each mature cavity ; but 
the extinct zoophyte produced successively three and four, and possibly a greater 
number: (4) that in Oculine, pallial developments at a distance from the supe- 
rior extremity of a branch are very rare, being exceptional rather than essential 
formations ; whereas in the cretaceous Anthozoon they are common and consti- 
tute a leading feature: lastly, the lamellz in the recent coral have a prevailing 
permanency, but in the fossil an extreme liability to decay. This aggregate of 
differences forbids, it is conceived, the chalk zoophyte being assigned to Ocu- 
lina ; and as the structures on which it depends do not, so far as the describer is 
aware, co-exist in any established genus, it is suggested that the word Diblasus 
might be adopted as a distinguishing term, founded on the twofold mode of 
budding, while in Oculina only one prevails, (cic bis, BAacto¢ germen). 
