involute

A curve that cuts all tangents of another curve at right angles; traced by a point on a string that unwinds from a curved object.

To roll or curl inwards.

Difficult to understand; complicated.

Having the edges rolled with the adaxial side outward.

(of shells) Having a complex pattern of coils in which younger whorls only partly surround older ones.

Turned inward at the margin, like the exterior lip of the shells of species in genus Cypraea.

Rolled inward spirally.