518 Dr. H. A. Nicholson and Mr. A. H. Foovd on a 



XLIX. — On a new Genus of Devonian Corals, with De- 

 scriptions of some Species of the same. By H. Alletne 

 Nicholson, M.D., D.Sc, Regius Professor of Natural 

 History in the University of Aberdeen ; and Arthur H. 

 FOORD, F.G.S., late of the Geological Survey of Canada. 

 [Plate XVII.] 

 [Contiuued from p. 400.] 



RhapMdopora stromatoporoides (continued). 



We are, however, entirely satisfied that the appearances 

 just described, upon which Schllxter founded his PacJiytlieca 

 steUtmicans, are of purely inorganic origin, and are the result 

 of mineralization. They are probably due to a finely fibrous 

 crystallization of the calcite, which has caused the dark-coloured 

 impurities in the matrix to arrange themselves in conformity 

 with the crystalline fibres. The radiating fibres thus produced 

 frequently extend from one tube to another, cutting through 

 the walls of the corallites, and so producing the beautiful 

 starry appearance which characterizes tangential sections, and 

 upon which Prof. Schlilter based his name of " sfeUimicans "■^. 

 This process of mineralization was potent enough to effect the 

 almost complete destruction of the tabulte, and in large part 

 that of the walls of the corallites as well, the latter remaining 

 in parts only obscurely discernible. Here and there this pro- 

 cess was not quite complete, and hence we sometimes find 

 spots in most vertical sections (PI. XVI. figs. 1 c and 7) in 

 which the visceral chambers have not been wholly occupied 

 by this infiltrated material, but have been partially filled with 

 clear calcite, and have the tabulee still left. Moreover, by the 

 extension of the radiating crystalline fibres from each centre 

 of crystallization through the walls of the corallites into con- 

 tiguous tubes were produced those curious dark transverse 

 bavs seen in tangential sections intersecting the walls of the 

 tubes, and regarded by Prof. Schlilter as of the nature of 

 filled-up mural pores. 



That the remarkable structure here in question is the result 

 of some such process of infiltration and crystallization as above 

 sketched out is rendered certain by the examination of a suffi- 



* A somewhat similar appearance is presented in tangential sections 

 of Mimotrypa qitndrata, Rominger, a Monticuli- 

 poroid from the Cincinnati group (Caradoc) of 

 Cincinnati, Ohio. In this we iind the visceral 

 cavities of the corallites traversed by irregular 

 lines, which radiate from each angle of the cell- 

 wall and meet in the centre (see woodcut). 1'he 

 same phenomenon is met with also in some other 

 palseozoic corals. 



