The figure below shows the distribution of samples containing the inarticulate brachiopod Trematis.

[ Trematis distribution

Trematis is a common inarticulate brachiopod in some parts of the MRV strata.

[ Trematis ]

Trematis Sharpe, 1848 [*Orbicula terminalis Emmons, 1842]
Circular to suboval in outline, biconvex; surface of both valves ornamented by small superficial pits variably arranged, commonly in rough quincunx or in lines radiating from beak; pedicle valve with subcentral beak, convex, but depressed posteriorly, open pedicle notch in depression, margins of notch straight or concave toward mid-line; pseudointerarea of brachial valve adnate to inner surface of valve, low median ridge variably developed separating 2 bean-shaped composite muscle scars.
M. Ord. - U. Ord., North America and Europe
Family Trematidae Schuchert, 1893
Beak of brachial valve marginal, protruding beyond pedicle valve; pedicle opening extending to posterior margin of pedicle valve in all growth stages.
M. Ord. - Dev.
Order Acrotretida Kuhn, 1949

Treatise on Invertebrate Paleontology, H283.