A concave mirror (latuscula) reflects an image with the true right and left, because the image is reflected twice (elisa bis), or because it is given a twist by the mirror.
"Mirrors that have small sides that are curved in the same degree as our sides send back images, right to our right and unreversed. Either since the image is carried across from mirror to mirror, and then flies to us having been twice reflected, or since the image is turned round when it approaches as the curved shape of the mirror turns it towards us" (Melville, DRN 4.311)
"All mirrors with bent sides, which have a shape curved like our own torso, send back to us, for that very reason, an image with our right side on the right, either because the image is transferred from one part of the mirror to another and then, after being reflected twice flies back to us, or because the image, as it gets to the mirror, is reversed -- the curving shape of the surface leads it to spin about towards us." (Johnston)
From Bailey’s commentary, page 1219: “Robin suggests that with the metal mirrors of antiquity the curved effect may have been produced by a number of small flat mirrors placed together at an obtuse angle. This would account for the diminutive, the plural, and the genitive speculorum, but… there is no evidence for the fact and there would be no difficulty in the bending of a metal mirror. Smith takes latuscula to refer to the ‘little sides’ of a jointed mirror.”
Pictured below in a non-reversing mirror is Hammon ("Amen Ra"), who’s warm-at-night, cool-by-day “Water of the Sun” spring in Cyrenaica (Libya), Lucretius talks about in DRN 6.848.