'56 



PAL/EONTOLOGY 



FIG. 45. APERTURAL MARGINS OF CEPHALOPODA. 



a, Discitoceras leveillianum (de Koninck), Carboniferous Limestone, 

 Clane, Ireland, a, Side view, showing gyrocone stage in centre, 

 passing into ophiocone ; there are indications of the radial and longi- 



