76 TABULATE CORALS. 



calcareous plate in a large number of the callces is a peculiar 

 feature in the species (PI. IV., fig. i a) ; but the same character 

 occurs generally in F. Forbesi, van tuberosa, Rom., and con- 

 stantly in F. turbinata, Bill. In all these forms the actual 

 characters of the operculum are the same, but in the last- 

 mentioned species they become more or less continuous, so as 

 to constitute a regular epithecal membrane, clothing the entire 

 under surface of the corallum. Thin tangential sections ex- 

 hibit no traces of septal ridges or tubercles. Similar vertical 

 sections show that the walls of the corallites are not thickened 

 as they approach the surface, and that the visceral chamber of 

 each tube is crossed by delicate horizontal tabulae, which are 

 usually complete, though occasionally incomplete ones exist as 

 well. Rominger says that the mural pores are " numerous." 

 So far as I have observed them in thin sections, they are uni- 

 serlal, and moderately close to one another. 



Formation a7td Locality. — Hamilton Group (Devonian), 

 Arkona, Ontario, and Erie County, N.Y. (Dr Rominger 

 states that it occurs also in the Corniferous Limestone.) 



