Anallagmatic

a. [ Gr. &unr_;; 'an priv. + &unr_; a change. ] (Math.) Not changed in form by inversion. [ 1913 Webster ]

Anallagmatic curves, a class of curves of the fourth degree which have certain peculiar relations to circles; -- sometimes called bicircular quartics. --
Anallagmatic surfaces, a certain class of surfaces of the fourth degree. [ 1913 Webster ]