210 PEOr. H. A. NICHOLSON AND DE. J. MUEIE ON THE 



radiating canals have been considered a generic character (dis- 

 tinguishing Ccenostroma) ; but they are present in forms of very- 

 different affinities, and it does not appear to us that they can be 

 used as a ground of generic distinction. They are especially well 

 developed in forms such as Stromatopora constellata, Hall, ^S*. ty- 

 pica, Von Eosen, S. astroites. Von Rosen, S. elegans, Von Rosen, 

 8. Schmidtii, Von Eosen, 8. granulata, Nich., Caunopora planulata. 

 Hall & Whitf , Stromatopora (^Coenostroma) incrustans, H. & W., 8. 

 {Ccenostroma) solidula, H. & W., Syringostroma densa, Nich., and 

 Syringostroma columnaris, Nich., &c. In the forms which one of us 

 has termed Syri/iigostroma (Nich. Pal. Ohio, vol. ii.) these radiating 

 canals are of specially large size, and in vertical sections their cut 

 ends are conspicuously seen as so many large rounded apertures. 



6. Vertical Water-canals. — Many Stromatoporoids show super- 

 ficial openings of very considerable size, which are apparently the 

 apertures of canals leading through the mass in a direction upon 

 the whole more or less perpendicular to the concentric laminae of 

 the mass. These canals have no distinct walls, and their apertures 

 vary in size from half a line or less up to a line or more. Their 

 function can hardly be any other than that of conducting the ex- 

 ternal water into the interior of the mass, or, as is more probably 

 the case, of carrying off the water which has circulated through 

 the colony, and their external openings have been compared with 

 the "oscula" of the Sponges. lu many forms these openings 

 have not been detected at all ; but they are very well marked in 

 others {e. g. in some specimens of Stromatopora striatella, 

 D'Orb. ?, in 8. Eindei, Nich., 8. tuherculata, Nich., 8. ponderosa, 

 Nich., and 8. ostiolata, Nich.)*. 



In a hitherto undescribed Stromatoporoid from the Trenton 

 Limestone, which appears to be clearly of generic importance 

 {Stromatocerium, Hall ?), the entire mass is perforated by vertical 

 canals, which are destitute of walls, and which are placed close 

 together and appear to communicate with large and irregular 

 lacunee in the mass, now filled with calc-spar. As will be subse- 

 quently mentioned, this singular form differs from all the normal 

 Stromatoporoids, not only in the number and closeness of the 

 canals just spoken of, but also in the total absence of vertical 



* These tubes have been supposed to be simply the work of boring Annelids 

 or other organisms ; but we cannot accept this view, and their number and regu- 

 larity of arrangement in S. ostiolata, Nich., would conclusively prove that they 

 belong, whatever ibeir nature may be, to the Stromatoporoid itself. 



