90 



by the extension of all planes in alternate dodecants above and 

 below the equatorial plane, as the shaded faces of Fig. 162. 



Forms 



na 



n i 



a : a : me 



K(hkil), K(khil). 



The faces represented by the poles 

 in Fig. 161 when extended will yield 

 the minus scalenohedron, Fig. 163, a 

 form bounded by 12 similar scalene 

 triangles. Six faces are grouped 

 around the extremities of the c axis. 

 Alternate edges are equal both as to 

 length and angle. The equatorial 

 edge of the di hexagonal pyramid is 

 replaced by 6 equal zigzag edges, 

 each of which is bisected by the ex- 

 tremity of a lateral axis. 



a : oo a t a : me 

 II. Rhombohedron of the first order, -; K(hohl), 



FIG. 163. The Minus Scaleno- 

 hedron, K(hkfl). 



K(ohhl). 



When the poles of Fig. 161 are moved into the planes of sym- 

 metry, a form, the rhombohedron of the 

 first order, Fig. 164, bounded by 6 simi- 

 lar rhombic faces, is the result. The form 

 is plus if the pole is moved into the plane 

 of symmetry lying between the ai and a 3 

 axes in front, and the minus form is pro- 

 duced when they are moved into the 



There are three 

 faces grouped 

 around each ex- 

 tremity of the c 

 axis, and three 

 equal edges. The 

 six zigzag edges 

 which are bi- 

 sected by the ex- 

 tremities of the 

 lateral axes are 



plane between a2 and 33. 



FIG. 164. The Minus Rhom- 

 bohedron of the First Or- 

 der, K (ohEl). 



FIG. 164 a. The Rhombo- 

 hedron of the Middle Edge 

 and Scalenohedron. 



