The inverse curve of Fermat's spiral with the origin taken as the inversion center is the lituus.
Fermat's Spiral Inverse Curve
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References
Lawrence, J. D. A Catalog of Special Plane Curves. New York: Dover, pp. 186-187, 1972.Referenced on Wolfram|Alpha
Fermat's Spiral Inverse CurveCite this as:
Weisstein, Eric W. "Fermat's Spiral Inverse Curve." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/FermatsSpiralInverseCurve.html