in a transverse direction proceeds with an acceleration which manifests itself in a curvature of the sides, replacing the straight borders of the original cone. In other words, the cross-section of the cone, or what we have been calling the generating curve, increases its dimensions more rapidly than its distance from the pole.
In the above figures, for instance in that of Cleodora cuspidata , the markings of the shell which represent the successive edges of the lip at former stages of growth, furnish us at once with a ãgraphã of the varying velocities of growth as measured, radially, from the apex. We can reveal more clearly the nature of these variations in the following way which is simply tantamount to converting our radial into rectangular coordinates. Neglecting curvature (if any) of the sides and treating the shell (for simplicityãs sake) as a right cone, we lay off equal angles from the apex O , along