Figure 158.—Mangaian pitching discs (Bishop Mus., C2819; series of 10): greatest diameters of series range from 114 to 121 mm., but cross diameters in individual discs are identical, except for two which have a difference of 3 mm.; thick edge (b,3) ranges from 18 to 21 mm. with an average of 19.8 mm.; lower border diameter averages 4 mm. less than upper border diameter; greatest thickness in center ranges from 49 to 53 mm. with average of 50.7 mm. a, upper surface with central cone (1). b, side view: 1, central cone; 2, concave plane of upper surface around cone; 3, thick circumferential edge; disc is stained black, c, d, light-colored disc showing upper surface (c) and side view (d).