of Crystalline Combinations. 409 
RHOMBOHEDRAL SYSTEM. 
Relations of Edges, &c. 
The acute terminal edges of the more acute pyramid are replaced by the obtuse 
terminal edges of the more obtuse pyramid in pairs. 
E. C. parallel to each other and to these terminal edges. (S. 7.) 
The alternate terminal edges of the isosceles pyramid are replaced by the faces, in 
pairs, of the scalene pyramid, meeting at its obtuse terminal edges. 
E. C. are parallel to each other and to these terminal edges. (S. T.) 
The alternate terminal edges of the isosceles pyramid are replaced by the faces, in 
pairs, of the scalene pyramid, meeting at its acute edges. 
E. C. are parallel to each other and to those terminal edges. _ (S. T.) 
See III. ea Face perpendicular to axis. 
See IV. 3.) E. C. horizontal. 
The lateral edges of the scalene pyramid are replaced by the faces of the prism. 
E. C. are parallel to each other and to these lateral edges. 
A pyramid with its summit replaced by a more obtuse pyramid. 
E. C. horizontal. 
22 een 
A regular prism terminated by a regular pyramid. 
E, C. horizontal. 
