VOL. I. PLATE X. 



FIG. 45. Derivation of isosceles four-sided pyra- 

 mids. 



Fro. 46. Derivation of the rhombohedron with 

 an infinite axis (a regular six-sided 

 prism). 



FIG. 4-7. Derivation of scalene six-sided pyramids-. 



FIG. 48. Derivation of isosceles six-sided pyra- 

 mids. 



FIG. 49. Combination of two rhombohedral forms, 

 producing EF and E'F, the Lines of 

 Combination. 



FIG. 50. Similar combination of three rhombohe- 

 dral forms. 



