The mouth is very narrow, and the halves of the under-jaw are not distensible.
Its two halves have each a negative and a positive scene.
Each valve is formed by the halves of contiguous carpels.
Make the umbrella shape by cutting a round cake in half and stacking the two halves on top of each other.
The pulley is in halves to facilitate fixing, and when in place the sections C are joined by plates E, bolted or riveted to the rim.