162 



THE DAWN OF LIFE. 



system ; and one of the most Eozoon-like I liave seen^ 

 is a specimen of the undescribed species already men- 

 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 fi^om 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, (b.) Inner wall, (c.) Outer wall, (n.) Nucleus, or primaiy 

 chamber. (v.) Internal cavity. 



this time these are accompanied by the Archaeo- 

 cyathids, and by another curious form, more nearly 

 allied to the latter than to Eozoon, the Recepta- 

 culites. These curious and beautiful fossils, which 

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

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

 but these coats are composed of square plates with 



