Distinguishing Rafinesquina

By Bill Heimbrock, Dry Dredgers

You can identify the Corryville member of the McMillan Formation by the presence of the abundant brachiopod, Rafinesquina nasuta. R. nasuta differ from R. ponderosa and R. fracta by having a distinct fold or "nose" at or near the center of the lip on the pedicle valve and by having a more cup-like concave brachial valve. These three species are shown below for comparison.

R. Ponderosa R. nasuta. R. fracta

Entire Cincinnatian Corryville m. Abundant in Fairview Fm

How to distinguish a Rafinesquina from a Strophomena

Lay the Rafinesquina and the Strophomena concave side down on a table top (bulging convex side up).

You can see the hinge on the Strophomena along the straight edge. On the Rafinesquina, the hinge is always concealed. Turn the Rafinesquina over with the concave side up and you will see its hinge.

Here is an illustration showing both sides of the Rafinesquina and Strophomena. You will never get these two brachiopods confused again!

Rafinesquina

Concave brachial valve with hinge line circled Convex pedicle valve

Strophomena

Concave pedicle valve Convex brachial valve with hinge line circled

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