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For some reason I wanted the name of a surface of revolution of a circular arc (less than $\pi$) around its chord. Wikipedia said "lemon" (https://en.wikipedia.org/wiki/Lemon_(geometry)) but sourced to MathWorld so I thought maybe MathWorld had made it up. Not so. Better sources say the same. And the surface for the complementary arc is an "apple".

It looks like a North American football but a "football" is a different surface of revolution, of constant positive Gaussian curvature: http://modellsammlung.uni-goettingen.de/index.php?lang=en&r=5&sr=17&m=182