132 Prof. TV. King on Pleurodictyum problematicum. 



the aggregated bases of tbe cells ; and it necessarily follows, that 

 the opposite or adhering surface is that to which the cell-aper- 

 tures are turned. It will now be understood why Pleurodictyum 

 problematicum is usually considered a coral. 



Respecting the vermiform appendage, Lyell, Milne-Edwards 

 and Haime consider it to be the remains of a Serpula, or a ser- 

 puUform bochj, and that our fossil is attached to it : on the con- 

 trary, Phillips describes the appendage in question as " a vermi- 

 cular cast in the tubule of some mollusk (?) which has perforated 

 the coral*." 



The "coral" itself struck Phillips as having considerable 

 resemblance to his Favosites megastoma and F. tenidseptaf, spe- 

 cies which De Koninck places in his genus Michelinia. Milne- 

 Edwards and Hairae include it in Foritidee, a family of their 

 division Zoantharia perforata J. But Dr. Roemer of Breslau ob- 

 jects to this collocation, and appears to have no doubt whatever 

 of its close relation to Michelinia, particularly the species M. 

 favosa^. 



Notwithstanding there may be different shades of opinion 

 among palseontologists respecting the nature of Pleurodictyum, 

 they all seem to agree in regarding it as a coral, and in con- 

 sidering the vermiform appendage as having no organic con- 

 nexion with it. At this stage of the present paper I feel it 

 necessary to announce, that I totally dissent from the views just 

 given : I cannot think that the fossil itself is a coral, properly 

 so called ; nor can 1 reconcile myself to any other opinion than 

 that the vermiform appendage is a structure constituting an 

 integral portion of its organization. 



Before stating my views, however, I purpose giving a some- 

 what detailed description of our fossil ; and in doing so I think 

 it best to describe its different parts in their original state, and 

 not as casts. 



Pleia^odictyum prohlematiaim is externally a nearly circular 

 concavo-convex discoid body, the under surface or base being 

 concave. It seldom exceeds an inch and a quarter in diameter 

 and about three-eighths of an inch in thickness. Its upper sur- 

 face slopes off regularly to the margin, which is thin. These 



* Tide " Figiu'es and Descriptions of the Palseozoic Fossils of Cornwall, 

 Devon, and West Somersetshire," p. 209. 



t Palaeozoic Fossils, p. 20. 



X Vide reference to these authors in a subsequent part of this paper. 



§ Dr. Roemer's views are advanced in the last edition of Bronn's 

 ' Lethaea Geognostica.' I have not been able to consult the details of my 

 friend's views, as given in this work ; but he gave me an outline of them 

 during a joyous dav we had together last September among the Stringoce- 

 phaluses, Megalodons, &c. at PafFrath. I hope he maj' be induced to give 

 an English dress to his views on Pleurodictyum in the ' Annals.' 



