A sort of in-between structure: the boards are adhered to the rounded textblock, and the covering paper is directly adhered to the spine and boards without turn-ins: a “stiffened wrapper” binding, perhaps. 
This binding demonstrates the fugitive nature of many natural colorants—the blue stones and red veins of the marble, visible on both boards, is completed vanished from the spine, with only the (likely) carbon black veins remaining.