89 



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 mak- 

 ing 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 al- 

 most hopeless. Hence, although I shall in general speak of these bo- 

 dies as alcyonia ; I am aware, that when their histories have been elu- 

 cidated 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 are 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 is 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 



