Species: Drepanella richardsonia (Miller, 1874)
Originally: Beyrichia richardsoni
Alternate Name: Drepanella richardsoni var. canadensis
Map point data provided by iDigBio.
- C5 Sequence (Lower Whitewater)
- Marginal ridge sickle-shaped.
- Submarginal ridge is thick and connects to anterior lobe.
- Two dorsal nodes/short, vertical ridges.
- Var. canadensis the same, but slightly more regular character of the superficial ornamentation of the test (shell).
Drepanella richardsoni from the Whitewater formation of Clarksville, Ohio, (OUIP 2121)
Ulrich and Bassler (1908)
- The youngest unquestionable Drepanella known is the D. richardsoni of the Richmond in Ohio. In this, the anterior end of the sickle-shaped submarginal ridge is thick and tends to connect with the basal part of the expanded and prominent, though still partially dissected, anterior lobe.
It has the two dorsal nodes or short, vertical ridges, and the sickle-shaped marginal ridge, which I regard as characteristic of the genus. A variety of D. richardsoni, differing from the typical form of the species mainly in the more regular character of the superficial reticulation of the test, occurs at Oakville, Ontario, in purple shales, referred by the Canadian geologists to the Hudson River Group. It might be called variation canadensis.