MODIFICATIONS. 261 



Simple and mixed decrements on the terminal angles of 



planes M. 

 General symbol P A P . 



Ifp I, mod. a is again represented, because 

 plane a results from a decre- 

 ment by one row on all the ter- 

 minal angles. 

 p ^> 1, class c is represented. 



Intermediary decrements on the terminal solid angles. 

 General symbol (B P B' q b'r bs) represents class d. 



Simple and mixed decrements on the lateral angles of 



the plane P. 

 General symbol E /p P E. 



l?p zn 1, the symbol represents mod. e. 

 p ^> 1, class h. 



Simple and mixed decrements on the lateral angles of 



the 'plane M. 

 General symbol P E' E p . 



If p =: 1, mod. e is again represented. 

 p ^> 1, class i is represented. 



Intermediary decrements on the lateral solid angles. 

 These are of two kinds. 



1. Such as produce the single planes on each 



angle, which are comprehended under class 



gi or class f. 



The general symbol is (D P B q Bf' q Fr). 

 If p ^> r, the symbol represents class f. 

 I>O - class g. 



2. Such as produce two planes on each angle 



belonging to class k. 

 General symbol (D P B q B"r Fs.) 

 In this symbol, the particular values of either of 



