CEPHALOPODA— ORTHOCHOANITES. 47 



Suborder Orthochoanites Hyatt. 



Orthoceratida. 



VIII. Orthoceras Breyn. 



Longiconic orthoceracones (rarely cyrtoceraconic), gently taper- 

 ing in the typical forms but more rapidly in Geisonoceras and 

 nearly pencil-shaped in Protobactrites; siphuncle centran or slightly 

 excentric — small in Geisonoceras; camerse rarely with deposits 



Fig. 1245. Orthoceras multicanieratum, natural section, and apical end of large 

 specimen, X Vi- (After Hall, Pal. N. Y., I. ) 



about the siphuncle. Surface smooth or with lines of growth. 

 Ordovicic-Triassic. 



13. 0. primigenium Vanuxem. * Ordovicic. 



Section circular, tapering rather rapidly; septa thin and closely 

 crowded, distant, one twenty-fifth diameter of shell. Surface 

 smooth. 



Common in the Beekmantown (Upper Little Falls dolomite) of 

 the Mohawk Valley and elsewhere in New York. 



