- CALCITES OF NEW YORK 25 
system of lateral edges coinciding with those of the rhombohedron from 
which they are developed. These forms are designated as scalenohedrons; 
the foundational rhombohedron is known as the rhombohedron of the middle 
edges. Every rhombohedron may be theoretically assumed as a rhombo- 
hedron of the middle edges for a series of scalenohedrons the number of 
which is limited only by the law of rational indexes. So for every positive 
rhombohedron a series of positive scalenohedrons, and for every negative 
rhombohedron a corre- 
sponding series of nega- 
tive scalenohedrons may 
be developed. Such a 
negative scalenohedron 
is shown in figure 13, 
developed from the nega- 
tive rhombohedron of 
figure 9, the vertical 
length of the scaleno- 
hedron in this case being 
three times that of its 
rhombohedron of the 
middle edges. The 12 
planes of every scaleno- 
hedron intersect in 12 
terminal or polar edges 
which are relatively long 
and short and are alter- Pig. 1 Pig 1 
nately disposed around the vertical axis. The longer of these whicn measure 
the more obtuse polar dihedral angles correspond in position to the planes 
of the rhombohedron of the middle edges, and the shorter of which, which 
measure the more acute of the polar dihedral angles, correspond in position 
to the terminal edges of the rhombohedron of the middle edges. As the pro- 
portion of the vertical length of the scalenohedron to that of its foundational 
