ANNELIDA— TUBICOLA. 



239 



Rochester (Niagaran) shale, New York. 



16. C. arcuatus Conrad. (Fig. 1524.) Siluric. 



Regularly tapering, sometimes more or less curved ; internal mold 

 shows a regularly increasing series of segments, abrupt and step- 

 like towards apex, sloping towards aperture. 



Fig. 1524. Cornulites arcuatus, two specimens, the larger X 2- (After Clarke 

 and Ruedemann, Guelph Fauna. ) 



Lockport and Guelph of New York; Upper Monroe of Michigan 

 and Ontario. 



V. Ortonia Nicholson. 



Small, solitary, conical, calcareous tubes, more or less flexuous, 

 thick-walled and cemented by the whole side to some foreign body ; 

 surface annulated, the rings overlapping as in Conchicolites of 

 which it is sometimes considered a synonym ; upper surface appar- 



FiG. 1525. <^) /^, Ortonia inter??tedia, greatly enlarged ; c, O. 7ninor, enlarged. 

 (After Nicholson.) 



ently cellular. (May be the young of Cornulites.) Ordovicic- 

 Carbonic. 



