32 CRYSTALLOGRAPHY. 
solid angles, as in the isometric octahedron. There may be, on 
the same crystal, faces of several octahedrons of these two series, 
differing in having their planes inclined at different angles to 
16. 

_ the basal plane. In figs. 5 and 7 there is one of these pyra- 
mids terminating the prism, and in figs. 6 and 8 the planes 
of two. In figs. 1 tc 3 there are planes of the same octahe- 
dron, but combined with the basal plane O; and in fig. 4 there 
are planes of two, with O. In fig. 9 there are planes of the . 
same octahedron, with planes of a square prism (7-2), and of an 
eight-sided prism (7-2). In fig. 18 there is the prism 77 com- 
bined with two octahedrons, and the hasal plane O; and in 
19 the planes of one octahedron with the prism JZ. 
Fig. 20 represents an eight-sided double pyramid, made of 
\ 
4) 
— 
« JA\ LT \ii| I 

equal planes, equally inclined to the base; and fig. 21, the same 
planes on the square prism 7-2. ‘lhe small planes, in pairs, on 
fig. 8, are of this kind. In fig. 22 the small planes 3-3 of 
fig. 8 occur alone, without planes of the four-sided pyramids, 
and therefore make the eight-sided pyramid, 3-3. 
This solid of sixteen planes has the largest number of similar 
pianes possible in the dimetric system, while the largest number 
in the isometric system (occurring in the hexoctahedron) is 
forty-eight. 
