A common irregular echinoid from the Turonian and Coniacian of the White Chalk. Holaster trecensis is superficially very similar but occurs in the Grey Chalk.
1). Sternotaxis plana (x2.5, White Chalk, Chanctonbury Hill, Randell Collection, RR0230). (A) View of the apical (upper) surface. (B) View of the oral (under) surface. The opening towards the anterior (top of the image) is the peristome.
A B C
2). Sternotaxis plana (x2.5, White Chalk (flint internal mould), Beachy Head, Randell Collection, RR0226). (A) Posterior (rear) view. The central opening is the periproct. (B) View of the apical (upper) surface. (C) Lateral (side) view, anterior (front) to the right.