CONTEMPOEARIES AND SUCCESSOES OF EOZOON. 157 



porous kinds are not very dissimilar from calcareous 

 sponges_, but tliey generally want true oscula and 

 pores_, and seem better adapted to shield tlie gelati- 

 nous body of a Foraminifer projecting pseudopods in 

 search of food^ than that of a sponge^ living by the 



Fig. 42. Stromatopora ritgoaa, Hall — Lower Silurian, Canada. 

 {After Billings,) 



The specimen is of smaller size than usual, and is silicified. It is probably 

 inverted in position, and the concentric marks on the outer surface are due 

 to concretions of silica. 



introduction of currents of water. Many of the 

 denser kinds^ however, have their calcareous floors so 

 solid that they must be regarded as much more nearly 

 akin to Foraminifers, and some of them have the same 

 irregular inosculation of these floors observed in Eo- 



