After considering alternative systemsfor classifying the basic shapes in his drawing and paintings, the author proposes additions to the classification system he presented in hisfirst article in Leonardo. One addition involves a specification of the way in which V-, Tand X-intersections in shapes in the pencil drawings are shaded. Another addition makes use of the Ostwald color system to specify the one, two or three colors employed in the paintings. Also he discusses 'contradictory' aspects of shapes in his drawings and presents a subclassification based upon whether or not the shapes can represent possible 3-dimensionalforms. In conclusion, he discusses how two classes of shapes in his drawings can be transformed into forms in bas-reliefs and raised-line embossings. He closes with a commentary on the interpretation of his works. I. CLASSIFICATION OF BASIC SHAPES In my first article published in Leonardo I presented examples of my drawings and paintings and a system for their classification [1]. Each of these works is based on a basic shape that is derived from one or more closed curves. In the classification system, each work is designated by four numbers: I, (the number of closed curves employed in deriving the basic shape) and 12, 3 and 14 (the number of line intersections of each of three types, V, T and X, respectively, in the basic shape). I realize that my choice of system is not unique. For example, I have considered Euler's theorem in graph theory, that states that, for a connected planar graph with v intersections and g connecting lines that partition a plane into r regions: v q + r = 2 [2, 3]. My 67 classified basic shapes (except 11-7, III-1 and III-9) are connected planar graphs [1, Figs. 1, 2]. For the 64 shapes I find that v = I2 + 1 + I, q = 12 3 1 + 2 I3 + 2 14 and r = 2 + I3 + I4. Thus, as classification criteria, the set (v, q, r) is equivalent to the set (12, 13, 14). However, implicit in my use of 13 and I4 is knowledge about branch continuity at Tand X-interesections, while use of Euler's parameters does not imply anything about the continuity of branches. Thus the set (I2, 13, 14) gives more descriptively useful information than the set (v, q, r). My classification system is made more specific by the inclusion of the parameter II, which gives 3dimensional information, because I visualize in space forms to which the basic shapes apply. In some cases I made models of forms from pipe cleaners before executing the corresponding paint*10533 Sierra Bonita Ave., NE, Albuquerque, NM 87111, U.S.A. (Received 8 Jan. 1980) ing or drawing (for example, 'III-12: Coil' (Fig. 6)). I will gladly supply further information about classification based on Euler's parameters to those interested. II. CLASSIFICATION OF SHADING IN BASIC SHAPES (DRAWINGS) In the case of the pencil drawings I have found a way to make their classification more specific by introducing the criterion of intersection shading to add to the four criteria I I, 1I, I3,4. I require that, at each branch of an intersection, one side of the line (branch) be shaded darker than the other side in order to delineate the boundary. Thus at a Vintersection, four kinds of shading are possible; at a T-intersection, eight; at an X-intersection, 16. These 28 kinds are presented in Fig. 1, where the shading employed indicates on which side of a branch in a drawing the shading is darker. I group together in blocks (Fig. 1) those kinds that are equivalent if the angle between successive noncontinuous branches is changed and/or if a mirror reversal of the whole intersection shading diagram is made. This reduces the essential total number of shading types for all 3 kinds of intersections to 10. Each block is indicated by a designation such as Va or Xd. Tables I and II show that I have employed all the shading types except Ta in drawings. However, a number of sketches exhibiting type Ta shading are in my notebooks, awaiting to be executed as full-scale drawings. Note that shading type Va corresponds to a tonal inversion, discussed earlier [1, Fig. 10]. The percentage occurrence of each shading type in completed drawings is as follows: Td: 31%; Va: 26%; Tc: 23%; Tb: 9%; Xd: 4%; Xc: 2.5%; Xb, Vb, X, and Ta: under 2%.