A Circle in a Circle (a rhymed riddle)

This is my entry to the Math Poetry Contest . Both the problem and the solution are part of the poem:

$\text{A small circle rolls inside of another,}$

$\text{The first is a fourth of the other's diameter.}$

$\text{A point of the lesser's is then traced about,}$

$\text{As it slides without slipping through its circular route.}$

$\text{A man named von Littrow has named it "Astroid",}$

$\text{Though its technical name is a tetracycloid.}$

$\text{So which of these shapes is the curve that I mean?}$

$\text{Here's a hint: it resembles a shape that you've seen!}$