AMORPHOZOA FROM THE SILURIAN AND DEVONIAN 



FORMATIONS. 



AMORPHOZOA. 



Genus STROMATOPORA. 



The genus Stromatopora comprises a number of somewhat enigmatical 

 fossils from the Silurian and Devonian formations which have sometimes 

 been referred to the Sponges, sometimes to the Foraminifera, and some- 

 times to the true Corals, though there can be little doubt as to their truly- 

 belonging to the first of these. The form of the fossils placed under 

 Stromatopora is not constant, though they usually occur as smaller or 

 larger spheroidal, pyriform, depressed, or amorphous masses, which some- 

 times attain a very considerable size. At other times they present them- 

 selves as more or less extensive, thinner or thicker expansions, the under 

 side of which is furnished with an epitheca. Whatever may be their 

 shape and size, the fossils properly referred to Stromatopora all agree with 

 one another in their intimate structure. They all consist, namely, of a 

 system of calcareous laminse, which are disposed concentrically round 

 one or more imaginary centers in the massive species, and are success- 

 ively superimposed in sheets parallel with the upper and lower surfaces 

 in the expanded forms. The concentric or horizontal laminte are sep- 

 arated *by interlaminar spaces, which are crossed by numerous delicate 

 perpendicular pillars or calcareous dissepiments, so that the entire mass, 

 when viewed in vertical section, appears to be composed of rows of quad- 

 rangular compartments or cells. The concentric laminte, further, are perfo- 

 rated in many, if not in all the species of the genus, by minute rounded or 

 sinuous apertures or pores, by means of which the successive interlam- 

 inar spaces are placed in communication with one another. Lastly, in 

 many, if not in all cases, the surface of the mass can be shown to exhibit 

 a comparatively small number of large, rounded apertures, leading down 

 into canals which perforate ij.s substance. 



Upon the whole, I can not doubt that the structures above-mentioned 

 as characteristic of Stromatopora are such as to necessitate the reference 

 of the genus to the Calcareous Sponges, rather than to either the Fora- 

 minifera or the Coelenterata. The concentric or horizontal laminte and the 



