Complex sentence: East of Hecataeus is a chain of tiny craterlets forming a line radial to Humboldt; these are designated the Catena Humboldt, named after the walled plain.
Split into simpler sentences: East of Hecataeus is a chain of tiny craterlets forming a line radial to Hunboldt crater. These are designated the "Catena Humboldt"; named after the walled plain.