MODIFICATIONS. 263 



The Octahedron with a rhombic base. 

 Fig. 312. 



Simple and mixed decrements on the terminal angles. 



Genera] symbol P A P . 

 p 



If p =z I, the symbol represents mod. a. 

 p ^> 1, class d. 



Intermediary decrements on the terminal solid angles. 



These are of four kinds, and require four general 

 symbols. 



We suppose the edges of the upper pyramid, which 

 are opposite to those marked with B and C, to be 

 denoted by b and c. 



Class b is represented by (Op B q b p c r ). 



Class c (B P C q c q br). 



Class e . . . (C P B q br c s : C P Br b q c s ). 



ClaSS f . . . (BpCqCr bs : Bp CrCq bs). 



Simple and mixed decrements on the angle E at the base. 



General symbol ^E 1 '. 



If p m 1, the symbol represents mod. n. 

 p ^> 1 , class q. 



