2.3. Stereo-micrometry
The shapes of the leading and trailing surfaces along the central line from top to base of mineralized radular tooth cusps were determined with the aid of a modified Hilger and Watts SB190 stereo-micrometer [2]. The stereo-micrographs used were recorded at tilt angles differences of 6–7° in an ISI SEM type DS 130. The resultant drawings of the central lines were used to measure the `curvature' of the leading and trailing surfaces, the curvature being defined as the angle between the tangent near the tip of the cusp and the tangent near the base.