arcus

Cum hoc arcus ejus extenditur, et primo sagittam in partem contrariam transmittit, et unum interficit.

The frustules are curved or arcuate (arcus, a bow) in the side view, oblong and narrowed at the ends in the front view.

Du Cange gives arcus sellae equestris as one of the meanings of circus.

They are called arcus horarum inequalium, as they shew the 'houres inequales.'

Its claim, as the parent of projectile implements, is recognized in the common etymology of arcus, arcualia—artillery.