Osteostraci genera

Cephalaspis (from , 'head' and , 'shield') is a possibly monotypic genus of extinct osteostracan agnathan vertebrate. It was a trout-sized detritivorous fish that lived in the early Devonian.

Hemicyclaspis ( or 'semicircle plate') is an extinct genus of primitive jawless fish, closely related to Cephalaspis, that lived in the Late Silurian (Pridoli) 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. Hemicyclaspis probably foraged the ocean floor for food.

Tremataspis is a genus of an extinct osteostracan agnathan from the Silurian period of what is now Estonia. thumb|left|Tremataspis schmidtii head and body armour at the Museum für Naturkunde, Berlin Tremataspis was about in length, and had an armored shield covering its head. Compared with its relatives, the shield was unusually elongated, covering the whole front of the body, and was more rounded in shape, an unusual characteristic for an osteostracan species. It is thought that Tremataspis used its rounder shield to burrow in the ocean floor, searching for food. Because the shield consisted

Dartmuthia is an extinct genus of primitive jawless fish that lived in the Silurian period. Fossils of Dartmuthia have been found in Himmiste Quarry, on the island of Saaremaa in Estonia. It was first described by William Patten.

Boreaspis (meaning "Boreas's Shield") is an extinct genus of osteostracan agnathan vertebrate that lived in the Devonian period.

Ateleaspis is an extinct genus of primitive ostracoderm fish that lived in the Silurian period (Wenlock Epoch) to the Lower Devonian. Like other ostracoderms, Ateleaspis had a head shield similar to that of Cephalaspis. Species from Silurian period were found in Norway and Scotland, but now has been found also in Siberia from Early Devonian period.