DIVISIONS OF GEOLOGICAL TIME 



389 



ZONES OF THE LOWER JURASSIC Continued. 



* The existence of several other hemerae in the Deiran and Mercian is indicated by Mr. 

 Buckman, but they are not definitely established, and are therefore omitted. See Quart. 

 Journ. Geol. Sac., vol. Ixxiii., pp. 257-327 (1918). 



t There is some uncertainty as to the position of this hemera ; it may be below 

 birchi. 



{ Lamellibranchs : no Ammonites are known outside the Alpine-Mediterranean province 

 before the planotbis hemera. 



