40 FOSSIL ALCYONIA. 



difference, that some substances will be placed before you, 

 which, not only cannot be referred to any particular known 

 species, but which would almost authorize the formation of 

 new genera for their reception. 



We shall proceed, however, as nearly as possible, accord- 

 ing to the generally accepted systematic classification ; and 

 shall derive what aid can be obtained, from the examina- 

 tions which have been made of living substances apparently 

 of a similar nature. It is intended, therefore, to endea- 

 vour to comprise, under the genus alcyonium or spongia, 

 the substances so accurately inquired into by M. Guettard, 

 as well as several others which have not been spoken of by 

 him, but are evidently of the same kind. 



Difficult to With respect to the classification of these bodies, a dif- 



distinguish al- ~ , , n . , , ._ . . 



cvonia .rom faculty alcnott insuperable presents itself ; since the cha- 



spong^sinthe racteristic marks by which the substances belonging to 

 these two genera are distinguished, in a recent state, are 

 frequently not to be discovered after they have sustained 

 the change of petrifaction, Previously, however, to pro- 

 ceeding further in an inquiry on this subject, it will be 

 proper to consider the nature of both alcyonium and of 

 sponge, and to ascertain what are the distinctive characters 

 of each. 



Characters of The alcyonium is an animal which assumes a vegetable 

 eacjoma. f orm ^ an( j wn ; cn j s either of a fleshy, gelatinous, spongy, 

 or leathery substance, having an outward skin full of cells, 

 with openings possessed by oviparous tentaculated hydra : 

 the whole substance being fixed to some other body by a 

 seeming trunk or root. 



Count Marsilli, who carefully examined not only the 

 physical, but the chemical properties of these bodies, ob- 

 serves that they are all surrounded by a porous leather-like 

 bark ; and that the interior substance is, in some, a jelly* 

 like matter, and in others, a mass of light ash coloured 

 acicular spines, which prick the hands on being handled, 

 in the same maimer as do the spines of the plant called the 

 Jndian fig, 



More minute- JDorjati, in his Essay on the Natural History of the Adri- 



ly examined at j c g ea) nag raa( i Cj m some respects, a more minute 'exa- 

 mination of the structure of two different species of alcy- 



gni.a 



