VOL. I. PLATE XV. 



A 'P 



FIG. 75. -. . Semi-tessular combination 

 2 % 



* f 



with parallel faces. 



A ^T^ 



FIG. 76. . - . Semi-tessular combination 

 2 2 



' / 

 with parallel faces. 



O Ci 



FIG. 77. Semi-tessular combination 

 2 2 

 P I 

 with inclined faces. 



FIG. 78. . Semi-tessular combination 

 2 2 

 P r 

 with inclined faces. 



FIG. 79. The saddle- shaped lens. 



FIG. 80. A rhombohedron with curved faces, 

 produced by composition. 



