ITS MODIFICATIONS. 197 







Class k. Lateral edges of prism replaced by single 

 planes. 



From the dissimilarity of any two adjacent edges 

 or angles of this class of primary forms, the modi- 

 fications, it will be remarked, are all single planes ; 

 some of the compound secondary forms belonging to 

 this class, are among the most difficult crystals to be 

 understood. 



ITS MODIFICATIONS. 



Primary form. A regular hexagonal prism. 



The planes M on M', measure 120. M on d, 150". 



The individuals belonging to this class will differ 

 from each other in the ratio of the edge G to the 

 edge B. 



Modifications. 



Class a. Solid angles replaced by single planes. 



Produces a six-sided pyramid on each summit, 

 resting on the edges of the prism. 



The new figures would be a series of dodecahedrons 

 with isosceles triangular planes. 



