220 



TABLE OF SECONDARY FORMS. 



Secondary forms. 



d. The planes being tra- 

 pezoids. 



Fig. 293. 



e. The planes 

 tagons. 



Fig. 294. 



pen- 



5. CONTAINED WITHIN SIX- 

 TEEN TRIANGULAR PLANES, 



which are generally sca- 

 lene, but may be isosceles 

 triangles. 



Fig. 295. 



How they may be derived. 



From the regular tetrahedron. 

 Modification b generally. 



, cube, Modification 



k. 



regular tetrahedron, 



particular Modification be- 

 longing to class d. 



From the octahedron with a 

 square base, Modification 

 d, ^, ?, &, or m. 



right square prism, 



Modification b. 



