Her arms (both missing from the elbow) could have held the knot of the mantle or perhpas a shell (if a shell, then this would be a nymph rather than Aphrodite). This version of Aphrodite is a Roman creation loosely based on the Hellenistic "Anadyomene" type.

Cf. plates 39 and 40 in Bieber, Ancient Copies: Contributions to the History of Greek and Roman Art, New York, 1977