AMOKPHOZOA FKOM THE SILURIAN AND DEVONIAN. 251 



centric crusts. 6. The entire organism must have attained a very large 

 size. 

 Position and locality : Corniferous limestone, Kelley's Island, Ohio. 



Genus SYRINGOSTHOMA, Nicholson. 



Sponge-mass calcareous, massive, composed of concentric laminte and 

 vertical pillars, which are so thickened and so amalgamated with one 

 another as to leave nothing but the most minute rounded cells. Lamin- 

 ated tissue traversed by numerous irregularly disposed horizontal canals, 

 which run parallel with the general surface, and are of comparatively 

 large sizj. Surface exhibiting more or less distinct rounded or vermicu- 

 lar apertures of small size. 



The fossils which I have included under this head may, perhaps, con- 

 stitute only a sub-genus of Stromatopora, but I have thought it best to 

 separate them in the meanwhile as a distinct genus. They agree with 

 the species of Stromatopora in their general form, and in the fact that 

 their structure is composed of laminated tissue ; but this tissue is extra- 

 ordinarily close and dense, and it is traversed by numerous irregular 

 horizontal canals or tubes, which run approximately parallel with the 

 surface, and which constitute a most conspicuous feature. Nothing of 

 this nature can be detected in the species of Stromatopora proper. 



The two following species of Syringostroma have come under my notice 

 as occurring in the Corniferous limestone of Ohio. 



Syringostroma densa, Nicholson. 



Plate 24, figs. 2, 26. 

 Sarcodeme apparently forming irregular masses or thick crusts, com- 

 posed of an exceedingly dense calcareous tissue containing very minute 

 cells. This tissue is probably essentially composed of successive con- 

 centric laminaj, separated by vertical dissepiments ; but its density is so 

 great that it may be regarded in practice as a mass of laminated cal- 

 careous matter in which excessively small but numerous cellular com- 

 partments are excavated. Not only are these cells extraordinarily small, 

 but they are only now and then arranged in horizontal lines, and they 

 often assume the form of minute tubuli passing through more than one 

 layer. Hence it i impossible to count the number of laminae or rows of 

 cells in a given vertical space, and it can only be said that the mass is 

 denser and the cells more minute than in any known species of Stromato- 

 pora, whilst, nevertheless, the composition of the whole out of concentric 



