VOL. i: PLATE XIII. 



FIG. 63. LJL. A right four-sided trapezo- 

 hedron. 



FIG. 64. _ >-;. A left four-sided trapezo- 

 hedron. 



FIG. 65. LJ_. A hemi-pyramidalform, ana- 

 logous to the tetrahedron, obtained 

 from a scalene eight- sided pyramid. 



FIG. 66. ^~~* ^ h e same, in inverse position. 



FIG. 67. Pyramidal combination. 



P. P + 1. (P)*. P -f oo. [P + oo]. 



abed e 



FIG. 68. Pyramidal combination. 



', ^-,P+3. IN- oo. [P+o>]. 



