Mr. E. J. Chapman on the Notation of Crystals. 333 

 MonocUnic System (continued). 



* In Dufrenoy's primary form, the plane c'is sometimes made an upper 

 back plane, and at other times an upper front one. When the latter is the 

 case, as in his figures of albite {Traits de Min., Atlas, pi. 166 to 171)» '^ will 

 equal A, and d AA, of the proposed notation. 



