In the 1980's Omas restyled its lines of pens.Top of the line was the big Paragon flanked by the 557 Ogiva.
The imprint on the barrel of Ogivas were originally OMAS 557/S (matching the imprint on Paragons whcih was 557/F) and later on it became Omas Extra.
Like Paragons, Ogivas were fitted with two tone nibs.
In the late 1980's a simplified version of the 557 Ogiva was introduced with a single cap band and without the band on the section. This pen belongs to this later production.
For more details about the evolution of these models, you can check the blog:
This Omas 557 Ogiva is pre-owned but in excellent condition.