that, as in its general form it resembles the last fossil, so, in its struc- 
ture, it is very nearly allied to the fossil represented Plate XI. Fig. 6. 
In both instances, the perpendicular lamella are numerous and small, 
and the transverse septa or processes very closely set, forming small 
polygonal interstitial cavities. 
A similar fossil is represented in Knorr’s elegant work, Vol. II. 
Plate F3, Fig. 1. A specimen of the same kind is also figured by 
Langius,* and is the figure erroneously referred to by Gmelin, as a 
turbinated medrepore, as mentioned in the seventh chapter ot the 
present volume. 
The peculiarity of structure observable in all these fossils seems to 
lead to the suspicion of their being all varieties of one species. Nor does 
the difference in their forms make so much against this idea as might at 
first appear ; since, as has been justly observed by Count de Marsilli, the 
extension of the substance of one species of alcyonium, in very different 
forms, is a circumstance of frequent occurrence. 
With a view to ascertain the nature of the internal structure of 
these bodies, I obtained a polished transverse section of the pedicle 
of one, which had somewhat of a ficoidal form, nearly corresponding 
with the one figured Plate XL Fig. 3. By this section, the alcyonic 
spongeous texture was rendered evident, as well as the transverse 
section of tubuli or small filamentary bodies. The alcyonium was 
then immersed in diluted muriatic acid, until the whole of the exter- 
nal surface was removed, when it was found that, instead of the per- 
pendicular and horizontal processes, forming regular square interstices, 
by their mutual decussations, they both appeared, directly on their 
departing from the surface, to have divaricated and ramified in vari- 
ous sportive contortions, thereby forming a reticular mass, evidently 
different from the substance of any of the other species, but approach- 
ing somewhat to that of the ficoid fossil, a perpendicular section of 
which is shewn Plate IX. Fig. 12. It is easy to conceive how accor- 
dant the structure, which had been here employed, must have proved 
* Historia Lapidum Figuratorum Helvetise, Tab. XII. P. 52. 
