2G GEOLOGICAL AND NATURAL HISTORY SURVEY OF CANADA. 



Corallitcs slender, usually irregularly four sided, closely approximated, 

 tortuous ; having a diameter of '5 to 'IS of a mm. The cell-apertures 

 exhibit three or four short eepta, usually the latter number. Tabula3 

 numerous and complete, about four or five in the space of 1 mm. Walls 

 thick. No opitheca has been observed. 



This species of Tetradlum is distinguished from all others by its large 

 size, very characteristic surface ornamentation, and laminated mode of 

 growth. 



Locality and Formation. — Capo Smyth, Lake Huron. Hudson River 

 Formation. 



Colkctor.^J)i\ R. Bell. 



