Rows 23 to 25—16 shells.

Row 26—15 shells (decrease 1 shell).

Rows 27 to 29—14 shells.

Row 30—13 shells.

Rows 31 to 33—12 shells.

Row 34—11 shells.

Rows 35 to 37—10 shells.

Row 38—9 shells.

Row 39—8 shells.

Row 40—7 shells.