Hypotrochoid vs. Epitrochoid: What's the Difference?

Hypotrochoid and Epitrochoid Definitions
Hypotrochoid
(geometry) A geometric curve traced by a fixed point on the radius line outside one circle which rotates inside the perimeter of another circle. Category:en:Curves
Epitrochoid
A geometric curve traced by a fixed point on one circle which rotates around the perimeter of another circle. Examples include the shape of the Wankel engine Category:en:Curves
Hypotrochoid
A curve, traced by a point in the radius, or radius produced, of a circle which rolls upon the concave side of a fixed circle. See Hypocycloid, Epicycloid, and Trochoid.
Epitrochoid
A kind of curve. See Epicycloid, any Trochoid.