branchia

Scutum and tergum articulated together, or overlapping each other; each branchia composed of a single plicated fold.

In these there are neither branchia nor osphradium, and the pallial chamber which retains its large opening serves as a lung.

Shell conical, not spiral; inferior pallial lobe transformed into a branchia.

Visceral mass and shell sinistral; inferior pallial lobe very prominent, and transformed into a branchia.

This has been called a branchial arm, not that it carried a branchia, but on account of its relation to the respiratory system.