162 THE DAWN OP LIFE. 



system ; and one of the most Eozoon-like I have seen, 

 is a specimen of the undescribed species already meij- 

 tioned from the Guelph (Upper Silurian) limestone of 

 Ontario, collected by Mr. Weston, and now in the 

 Museum of the Geological Survey. I have attempted 

 to represent its structures in fig. 44. 



In the rocks extending from the Lower Silurian and 

 perhaps from the Upper Cambrian to the Devonian 

 inclusive, the type and function of Eozoon are con- 

 tinued by the Stromatoporge, and in the earlier part of 



Fig. 46. Beceptaculites, restored. {After Billings.) 



(a.) Aperture. (6.) Inner wall, (c) Outer wall, (n.) Nucleus, or primary 

 chamber. (v.) Internal cavity. 



this time these are accompanied by the Archgeo- 

 cyathids, and by another curious form, more nearly 

 allied to the latter than to Eozoon, the Becepta- 

 culites. These curious and beautiful fossils, which 

 sometimes are a foot in diameter, consist, like Archaeo- 

 cyathus, of an outer and inner coat enclosing a cavity ; 

 but these coats are composed of square plates with 



