VOL. I. PLATE IX. 



FIG. 41. P. Fundamental pyramid of the hemi- 



prismatic system. 

 FIG. 42. P. Fundamental pyramid of the tetarto- 



prismatic system. 

 FIG. 43. Derivation of two subsequent rhombo- 



hedrons from each other. 



FIG. 44. Transverse sections of four consecutive 

 rhombohedrons, having the same hori- 

 zontal projection. 



