BASE, AND ITS MODIFICATIONS. 135 



Class /. Edges of the pyramids replaced by tan- 

 gent planes. 



The new figure resulting from this modification 

 would be an octahedron with a square base, but more 

 obtuse than the primary. 



Class m. Edges of the pyramids replaced by two 

 planes. 



Class m would produce eight-sided pyramids simi- 

 lar in character to those resulting from class d. 



Class n. Edges of the base replaced by tangent 

 planes. 



