An Art Deco Gold Ring With A Roman Bloodstone. Venus Anadyomene With Cupid.

Intaglio: 1.2 x 0.9 cm (0 ¹/₂ x 0 ³/₈ inches)
Mounting: gold (18k) UK size P ^1/2 (resizeable); total weight 8,48 gr
Roman imperial, 2nd century A.D. on an Art Deco ring, ca. 1920.

The stone shows Venus, the goddess of Beauty, standing partially naked in a contrapposto and holding her hair with both hands. The lower part of her body covered with a delicate folded drapery.
Next to her, Cupid, the god of Love hands her an attribute (possibly a mirror). 
Intimate toilet scene with allegorical meaning to youth and eternal love. 

We can find this specific scene on some ancient gnostic gems with magical inscriptions engraved on the reverse.
The Art Deco ring is formed by a rounded hoop, flatten within, with cutted shoulders sustaining a beautiful bezel with geometrical pattern. Beneath, are engraved 3 capital letters— 'AMI',  perhaps an abbreviation of a motto, or a hidden personal reference of the previous owner. 

For similar magical intaglios see
Intaglio BNF, Paris inv. 58.2238
Intaglio BM, London  inv.n. 1986,0501.130