VOL. I. PLATE XL 



FIG. 51. 2 (P) m . A di-pyramid. 

 a,a' 9 b,V 



FIG. 52. +t a \. A three sided pyramid, 

 - % (.a ) 



formed by alternating pairs of faces of 

 a di-rhombohedron. 



FIG. 53. | a I . A right three-sided trape- 



zohedron, containing on both ends 

 faces of the same pyramid. 



b 



FIG. 54. . | b | . A left three-sided trape- 



zohedron of the same kind. 



FIG. 55. . 1 ^, } . A right three-sided tra- 



pezohedron, the pyramid from which 

 the lower faces are derived being in 

 inverse position from that to which 

 the upper ones belong. 



FIG. 56. iJ ffiT { * i . A left three-sided trape- 

 / 2 l 6 ^ 



zohedron of the same kind. 



