CONTEMPORARIES AND SUCCESSORS OF EOZOON. 161 



mens are from the older part of the Lower Silurian 

 series ; but unfortunately their minute structures are 

 not well preserved. 



In the Silurian and Devonian ages, these Stromato- 

 porae evidently carried out the same function as the 

 Eozoon in the Laurentian. Winchell tells us that in 

 Michigan and Ohio single specimens can be found 

 several feet in diameter, and that they constitute the 

 mass of considerable beds of limestone. I have myself 

 seen in Canada specimens a foot in diameter, with a 

 great number of laminae. Lindberg* has given a most 

 vivid account of their occurrence in the Isle of Goth- 

 land. He says that they form beds of large irregular 

 discs and balls, attaining a thickness of five Swedish 

 feet, and traceable for miles along the coast, and the 

 individual balls are sometimes a yard in diameter. In 

 some of them the structure is beautifully preserved. 

 In others, or in parts of them, it is reduced to a mass 

 of crystalline limestone. This species is of the Cceno- 

 stroma type, and is regarded by Lindberg as a coral, 

 though he admits its low type and resemblance to 

 Protozoa. Its continuous calcareous skeleton he 

 rightly regards as fatal to its claim to be a true 

 sponge. Such a fossil, differing as it does in minute 

 points of structure from Eozoon, is nevertheless proba- 

 bly allied to it in no very distant way, and a successor 

 to its limestone-making function. Those which most 

 nearly approach to Foraminifera are those with thick 

 and solid calcareous laminae, and with a radiating canal 

 * Transactions of Swedish Academy, 1870. 



