62 



NORTH AMERICAN INDEX FOSSILS. 



50. K. orus (Hall). (Fig. 1266.) Siluric. 

 Larger than preceding and with coarser and more distant longi- 

 tudinal ridges. 



Niagaran of Wisconsin, Indiana, etc. 



51. K. darwini (Billings). (Fig. 1267.) Siluric. 



Fig. 1267. Kionoceras darwini. 

 (Pal. Ohio.) 



Fig. 1268. Orygoceras cornu-oryx^ 

 internal mold and specimen with shell 

 partly preserved. (After Ruedemann.) 



Slightly curved ; annulations mostly near apical end, faintly 

 visible in older portion ; longitudinal ridges much as in K. angu- 

 latum but generally with intercalated, finer ones. 



Niagaran (Guelph) of Ontario and New York. 



XV. Orygoceras Ruedemann. 



Orthoceracones with subcircular or depressed oval section; 

 annulations only internal; siphuncle excentric and tubular as in 

 Orthoceras. Ordovicic. » 



