In the 1980's Omas restyled its lines of pens.

Top of the line was the big Paragon, named 557/F flanked by the 557/S 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 simply Omas Extra. Both early Paragons and Ogivas had a serial number imprinted on the barrel, which was later on abandoned. Paragons, and Ogivas were fitted with two tone nibs.

In the late 1980's a simplified version of the 557/S Ogiva was introduced with a single cap band and without the band on the section. 

For more details about the evolution of these models, you can check the blog:

https://www.tenpen.it/article/milord-paragon

It is fitted with a very pleasant 18 ct B nib, which is smooth and very pleasant  to use.