122 



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 lamellae 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 F 3, 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 madrepore, as mentioned, in the seventh chapter of 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 alcyo- 

 nium, 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 XI. 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 accord- 

 ant the structure, which had been here employed, must have proved 



* Historia Lapidum Figuratorum Helvetia;, Tab. XII. p. 52. 



