The figure below shows the distribution of samples containing the spiriferid brachiopod Zygospira.

Zygospira is an uncommon spiriferid brachiopod in the MRV strata.

Zygospira Hall, 1862 [*Atrypa modesta Say, in Hall, 1847] [=Anazyga Davidson, 1882]
Unequally biconvex, elongate or transverse shells, pedicle valve more convex, commonly with ventral fold and dorsal sulcus, simple plications; foramen mesothyridid, deltidial plates conjunct, beak ridges strong and well defined. Dental plates lacking; hinge plates disjunct, parallel medially, diverging ventrally, and supported by myophragm; spiralia directed submedially with dorsal inclination; jugum a simple band curving toward middle of valve, origin of jugum variable, anterior or posterior.
M. Ord. - U. Ord., ?L. Sil., Europe (Great Britain) - North America
Family Atrypidae Gill, 1871
Shell plicate or costate.
M. Ord. - U. Dev.
Order Spiriferida Waagen, 1883.

Treatise on Invertebrate Paleontology, H634.