Marginix is an extinct genus of brittle star in the family Encrinasteridae that lived during the Devonian period in South America and Africa.

In 1916, a study by Rudolf Ruedemann describing some fossil material sent from Cerro Blanco, Jachal, Argentina to John Mason Clarke at the New York State Museum was published.

The fossils, then thought to represent starfish remains, were recognized by Ruedemann to represent two new species, one of which he thought was a member of the genus Encrinaster and named Encrinaster yachalensis, the specific name referring to Jachal.

Realizing this, Sergio Martínez and Claudia del Río renamed the genus again to Marginix in 2015.

[4] The following species are currently assigned to the genus Marginix: This prehistoric Ophiuroidea-related article is a stub.