of Crystalline Combinations. 415 
SQUARE-PYRAMIDAL SYSTEM. 
Relations of Edges, &c. 
A regular four-sided prism, terminated by a pyramid in a diagonal position. 
E. C. parallel to the rhombic section of the pyramid through its diagonal. 
Faces of pyramid are rhombs, and faces of prism, if they are complete. 
Faces of prism are rhombs if they do not meet: if they do, faces of pyramid are rhombs. 
A regular eight-sided prism. 
The forms are in a parallel position. 
The faces of the four-sided pyramid replace the apex of the eight-sided one, and are 
thombs. 
E. C. parallel to the terminal edges of the four-sided pyramid. (B). 
The forms are in a diagonal position. ° 
The faces of the four-sided pyramid replace the apex of the eight-sided one, and are 
rhombs. 
E. C. parallel to the terminal edges of the four-sided pyramid pQr (B). 
{- P ; Qn is the same as a form derived by the law of scalene derivation from pQr, 
n+1 
n—-1 
according to 
i. (S. T.) 
A face perpendicular to axis. 
E. C. horizontal, 
A regular square prism in a parallel position, with an eight-sided pyramid. 
The faces of the prism appear as rhombs replacing four lateral angles of the pyramid. 
The form of these rhombs depends on 7. 
A regular square prism in a diagonal position with an eight-sided pyramid. 
The faces of the prism appear as rhombs replacing four lateral angles of the pyramid. 
The form of these rhombs is similar to that of the section of the pyramid qQ through 
its diagonal, and E, C. parallel to this section. 
Vol,.M.~Part I, 3H 
