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as hardly to be detected, is very likely, in the fossil substance, to be 
still more difficult to be made out. Indeed, from this indistinct- 
ness of the radiation, much difficulty appears to have arisen in making 
the necessary distinction between even the recent sponges and 
alcyonia; the graduation from the perfectly radiated opening of the 
alcyonium, to the plain opening of the sponge, being so gradual and 
imperceptible, as to render it a difficult task, even where the substances 
are in a recent state, to draw the line where alcyonium ceases and 
sponge begins. But here is not the whole of the difficulty : several 
of the fossils, which will be presently described, possess some of the 
characters of ascidia and actinia, with those of the sponge or alcyo- 
nium ; thereby rendering their distinct and correct classification almost 
hopeless. Hence, although I shall in general speak of these bodies as 
alcyonia, I am aware, that when their histories have been elucidated 
by the inspection of more illustrative specimens, several of them may 
claim other designations. 
The consideration of another circumstance leads to the necessity 
of giving up every idea of distinguishing the alcyonia from the sponges, 
whilst in a mineralized state. Among the fossil zoophytes which claim 
a situation under one or the other of these genera, by far the greater 
number are such as ai e so totally different, from any known species of 
either alcyonium or sponge, as to render it almost impossible to de- 
termine under which genus they ought to be placed. Under these 
circumstances, you must perceive that the attempt to separate these 
fossils, by specific distinctions, at present, would be hopeless : it can 
only be effected when, by additional observations, their nature and 
forms are more perfectly known. 
When it is recollected what very considerable variations in form, are 
found to take place in the recent individuals, of the several species into 
which these substances are divided ; and when it was considered, that 
whilst passing into a mineralized state, their figure and appearance 
may be also much changed, it may be suspected that hardly any op- 
VOL. II. N 
