218 



PEOr. H. A. NICHOLSON AND DR. J. MUEIE ON THE 



interspaces between which are crossed with more or less regu- 

 larity by well-developed and complete radial pillars, producing 

 the tissue of regular quadrangular cells which forms such a 

 characteristic feature in vertical sections of forms of this type. 

 Among the forms which we have examined ourselves, we may 

 mention as belonging to the same type — S. (Goenostroma) granu- 

 lata, Nich., S. tuberculata, Nich., S. ostiolata, Nich., /S. nulli- 

 poroides, Nich., S. nodulata, Nich., and/S^. {Ocenostroma) discoideum, 

 Lonsd. sp. It appears, also, that S. typica, Von Eosen, and >S', 

 expansa, Hall and Whitfield, should be placed here ; and there 

 are doubtless many other forms with whose internal structure 

 we have but an imperfect acquaintance. 



Fig. 4. 



Stromatopora {Caunopora) perforata. 



a. Fragment showing the osculiferous tipper surface, of natural size. b. 

 Vertical section exhibiting internal structure, magnified, c. Another vertical 

 section, very slightly enlarged, showing more especially the perpendicular canal- 

 structure. From the Corniferous limestone, Port Oolborne, Ontario. (After 

 Nicholson.) 



"While all the above agree in the peculiar form and arrange- 

 ment of the minute elements of the skeleton, they present various 

 differences in structure, some of which will probably be found to 

 be of sufficient importance to serve as a basis for the establish- 

 ment of subgenera. 



S. polymorpJia, Goldfuss, and S. typica, Von Eosen, exhibit 

 very clearly two sets of pores, which penetrate the concentric 

 laminae and open on the surface. Most of these pores are very 

 minute, and may perhaps be compared with the " inhalant aper- 

 tures " or "pores" of Sponges; while others are much larger, 



