Figure 44. Adz of Tridacna shell: width of the shell, and thickness in millimeters. a, front formed of inner nacreous surface of shell, concave longitudinally and transversely, dotted parts of butt and cutting edge ground down to flatten concavity of shell, cutting edge curved, and grinding forms straight surface in front; b, back, showing rough external surface of shell with some grinding to remove black external layer—dotted part near lower edge marks forward grinding to form short cutting edge; c, right side, showing longitudinal curve with concavity in front, thickness of 11 mm. due to the transverse curve, with actual thickness of shell in thicker parts ranging from 7 to 8 mm. Length, 90 mm.