genus of extinct brachiopods, or lamp shells, found as fossils in Middle Silurian to Lower Devonian marine rocks (the Silurian Period ended and the following Devonian Period began about 416 million years ago). The genus Eospirifer is closely related to other genera included in the brachiopod group known as the spiriferids, a formerly important group of animals. Eospirifer has a moderate-sized shell bearing fine, radiating ribs (costae). Arcuate (bow-shaped) growth lines are also present.