SPONGIDA. 



139 



are disposed to take a different view of the affinities of the 

 " Stromatoporoids," and to place them among the Hydrozoa, 

 in the sub-class of the " Hydrocorallines." This view seems 

 to be based principally upon the curious Devonian genus 

 Caunopora, which differs from Stromatopora proper in many 

 important respects, and the structure of which in spite of 

 many able researches has still to be fully worked out. 



Fig. 36. a, Part of the under surface of Stromatopora tuberculata, showing the wrinkled 

 basement membrane and the openings of water-canals, of the natural size; 6, Portion of the 

 upper surface of the same, enlarged; c, Vertical section of a fragment, magnified to show 

 the internal structure. Corniferous Limestone, Canada. (Original.) 



Upon the whole, therefore, we must at present regard the 

 position of Stromatopora and its allies as uncertain. 



In the genus Archceocyathus (fig. 37), we have a group of 

 singular fossils which have been described by Mr Billings 

 from the summit of the Cambrian and the base of the Lower 

 Silurian (Potsdam Sandstone and Calciferous Sand-rock), in 

 North America, and have been subsequently investigated by 

 Principal Dawson. The general form of the fossils herein 

 included is that of a hollow cone or hollow cylinder, enclos- 

 ing a large cup - shaped cavity, and tapering towards one 

 extremity, which was presumably fixed to some foreign body. 



