12 Dr. H. A. Nicholson on the Genus Stromatopora. 



and by the finer and more minute character of the surface- 

 granulation. The number and closeness of the oscula also 



■-':^ 



stromatopora perforata : a, a fragment, showing the osculiferous upper 

 surface, natiiral size ; b, a fragment magnified, to show the internal 

 structure; c, vertical section of a fragment, showing the form and 

 course of the canals, uatm'al size. 



separate this form from S. granulata, in which the oscula arc 

 remote, and often cannot be detected at all, though in other 

 respects the surface-characters of the two are very similar or 

 even identical. The under surface of 8. lyerforata is still un- 

 known ; but the fossil forms thinner or thicker crasts, often 

 covering pretty extensive surfaces, the thicker expansions 

 being composed of a succession of crusts superimposed one 

 upon the other. 



Locality and Formation. — Rare in the Corniferous Lime- 

 stone of Port Colborne. Collected by the author. 



4. Stromatopora Hindei^ Nicholson. 



Fossil forming thin crusts or subhemispheric masses com- 

 posed of successive concentrically disposed strata, each stratum 

 made up of parallel calcareous laminas separated by interspaces. 

 Sometimes the component lamiuse of each stratum are parallel 

 with the upper and lower suifaces of the stratum or nearly so ; 

 but more commonly they are oblique to these sm-faces. The 

 result of this is that the interspaces between the lamina3 open 

 on the surfaces of each stratum as so many elongated and 

 oblique apertures, which have usually the form of fissure-like 

 sinuous slits, but sometimes present the a])j)earance seen in 

 v/eathered specimens of Alveolites. The laminie of ca(ih stra- 



