convolute

The two first have zigzag passages; the third, channels running in convolute curves.

The passages here run in convolute curves, the one winding in a spiral to the centre, the other receding from the centre.

They resemble the Ammonites in internal structure, but instead of being spirally convolute they are merely curved like a horn.

The more decidedly convolute species with hidden spires are the Atys, Montf.

A spiral shell is said to be discoidal, when the whorls are so horizontally convolute as to form a flattened spire.