The Half-Mourner

Not a day for butterflies but I found this dead marbled white in the conservatory this morning. I looked it up in my copy of the History of British Butterflies (1852) by the Rev. Francis Morris and found it was also known as the 'Half-Mourner' and the 'Marmoress'. Half-mourner strikes me as typically Victorian but I have no idea what Marmoress refers to and Morris doesn't say.