OF CENTRAL CANADA PART IV. 225 



Stromatopora is of not uncommon occurrence in our Silurian for- 

 mations. It has been referred to the Foraminifera, the Sponges, 

 the Zoantharia and the Hydrozoa. It forms hemi- 

 spherical or more or les^* irregular masses, often 

 many inches in diameter, made up of numerous 

 concentric, wavy lamellae. Our most common 

 species is the S. rugosa, found especially in the 

 Trenton (including the Black River) formation of 

 various parts of Ontario and Quebec. Another 

 closelv related species S. concentrica occurs in the 

 Niagara formation. Trenton Formation - 



Archeocyathus occurs in expanding, beaker-like or horn-shaped 

 forms, with deep central cavity, the sides of which are marked with 

 what appear to be the openings of radiating canals. The form has 

 thus a general resemblance to a Zaphrentis or other cyathiform coral. 

 Species have only been found, at present, in the Potsdam and Cal- 

 ciferous formations of the Straits of Belle Isle and the Mingan 

 Islands of Eastern Quebec. Eospongia is mostly pyriform or sub- 

 globular in aspect, with central depression and radiating pores. 

 Species occur in the Chazy formation of the Mingan Islands. 

 Astylospongia occurs in small, globular or sub-globular forms, without 

 a central cavity, or with only indications of this ; but with radiating 

 lines or pores at the somewhat flattened upper portion, and without 

 any signs of a stem-attachment at the under side. Species have been 

 found in the Trenton and Niagara formations, but are of compara- 

 tively rare occurrence. 



SUB-KINGDOM III. 

 C03LENTERATA. 



The typical coelenterates are distinguished from lower forms by the 

 possession of a distinct body-cavity with single mouth-opening ; and 

 from higher forms, by the absence of a distinctly separated stomach 

 the body-cavity and stomach being practically identical. The 

 mouth-opening is surrounded by tentacles. All coalenterates are 

 aquatic types. They may be classified conveniently, as shewn in 

 the annexed tabular view : 

 15 



