Cardinal area probably narrow and small. The cardinal process protruding into the pedicle foramen. Teeth large and conspicuous. The specimen found is an internal mold, but it shows that the surface of the shell was covered by numerous radiating striae which were crossed by concentric growth lines.
The interior shows a strongly impressed muscular impression on the pedicle valve. This resembles very closely the similar impression in R. vanuxemi but differs from it in the conspicuous divisions characteristic of that species. In the species here described this muscular impression extends slightly more than half the length of the shell and is divided by a prominent median ridge. The brachial valve shows a slight rounded median ridge which extends about a third of the length of the shell and is continued backward into the cardinal process. The muscular impression in this valve is poorly defined. The crural processes are prominent as in R. vanuxemi. While this form resembles closely R. vanuxemi it is somewhat intermediate between that form and R. penelope.
Horizon and locality.—Amherstburg dolomite, Stony Island Dry Cut in Livingston Channel, Detroit River, near Trenton, Michigan.
Schizophoria prima n.sp.
Plate II, Fig. 3
Shell transversely elliptical or roundly quadrate, moderately convex. Hinge line approximately straight and equal to about half the width of the shell.
Brachial valve unknown. Pedicle valve with rather prominent umbonal region and sloping abruptly to the cardinal area and extremities. In other directions from the umbonal area the valve is more or less flattened (possibly accidentally) but abruptly curved downward at the margins. The front third shows a broad ill-defined sinus which makes but a slight impression on the front margin. Surface marked by fine radiating striae, which are poorly shown on the internal mold. Concentric growth lines are also visible.
The internal impression of the pedicle valve shows a rather small subquadrate muscular scar, which is bordered by a deeply impressed
