M and N
denote figures somewhat resembling mountain peaks, M signifying an outline like that of a typical volcanic peak, while N, though similar, ends in a rod-like form, as of a flag-staff on a mountain top. Invert either of those typical forms and they can be read as before.
A curved cliff-like form, like a wave with a curling crest, may be indicated by the Spanish ñ.
L and R
denote loops in which curvatures are apt to occur. L is a loop, the axis of which is straight, while R is one the axis of which is curved or crooked.
Note that if the legs of a loop widen out beyond the parallels, it is no longer a loop, but a bow or a mountain. They may narrow again and yet remain loops till at last they coalesce, when the figure is transformed into a spindle or a battledore (T, D; or K, G). If the bend is more than that of a right angle, it comes under a new definition, and has some qualities of the whorl or spiral, but is more complex. This need not be entered upon here.
S and Z
I have used these two consonants to indicate certain patterns of a sinuous, undulating, or zig-zag type, the sinuous or purely undulating figures coming under S, but under Z if there is at least one distinct angularity in the pattern.
X
This letter, long familiar to the student of algebra as the symbol of the undetermined, I have reserved for the inclusion of various nondescript and anomalous patterns. Those might become fairly numerous in an extensive register, and in such case there would, no doubt, be found a good basis for fresh sub-classification.