'half-round shield' or 'semicircle plate') is an extinct genus of primitive jawless fish, closely related to Cephalaspis, that lived in the Late Silurian (Pridoli)[1] to Devonian period in what is now Europe and North America.

A typical cephalaspid, Hemicyclaspis had a heavily armored, shovel-shaped headshield.

It is thought to have been a better swimmer than most of its relatives because of its powerful tail, stabilizing dorsal fin and the keel-shaped hydrodynamic edges of its head shield.

[2] Hemicyclaspis grew to a length of 5 inches (13 centimeters) and would most likely have fed on particles from the muddy sea bed.

This article related to a Devonian jawless fish is a stub.