32 NEW YORK STATE MUSEUM 
the edge B above at a distance from E twice that of the intercept on B 
below. 
The negative rhombohedron —4$R shown in figure 11 and which bevels 
the B edges of the unit rhombohedron is designated in Lévy’s notation as b'. 
A negative rhombohedron more obtuse than —4R would incline toward 
A and would be indicated by the symbol a with a fractional ex ponent less 
than 1 since a‘ represents the basal pinacoid. 
Continuing along the same line the positive rhombohedrons having an 
inclination between the basal pinacoid and the unit rhombohedron, that is 
those having a coefficient of R (Naumann) which is less than 1, would be 
indicated in Lévy’s notation by a with an exponent greater than 1. Sim1- 
larly negative rhombohedrons having a steeper inclination than R are 
represented in the Lévy symbols by e with varying exponents. Positive 
rhombohedrons are called in this notation Rhomboedres directs and negative 
rhombohedrons Rhomboedres inverses. Scalenohedrons which bevel the 
edges B are indicated by b with an exponent greater than 1 and scaleno- 
hedrons which truncate the angles E in such a way that the intersections on 
the edge B and on one of the edges D measured from E are equal, are indi- 
cated by e with an exponent greater or less than 1. For other scaleno- 
hedrons, that is for those whose intersections on the three intersecting edges 
are unequal, the general symbols bi bi br, bi be di and di dk br apply, the 
exponents +++ and + being the corresponding Miller indexes for the form. 
In general, since the edges of the unit rhombohedron are parallel to the 
Miller axes the exponents of the Lévy symbols are the reciprocals of the 
corresponding Miller indexes. 
In many of the older papers on the crystallization of calcite a system of 
notation devised by F. Mohs! is employed. This system is now obsolete 
but inasmuch as many of these papers are of value as touching the early 
recognition of well known forms, the symbols of Mohs are given in correla- 
tion with those of Naumann, Bravais, Miller and Lévy in the table on 
pages 38-50. 
*Mohs, F. Grundriss der Mineralogie. Dresden 1822-24. 
