Species: Trochonema madisonense Ulrich & Scofield, 1897
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1897 Trochonema madisonense Ulrich, Geol. Minnesota, 3, pt. 2, p. 1051, pl. 77, figs. 23-25.
1908 Trochonema madisonense Cumings, 32d Ann. Rep. Dep. Geol. Nat. Res. Indiana, p. 976, pl. 42, figs. 1-1b.
Map point data provided by iDigBio.
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- C5 Sequence (Whitewater)
Identification in Hand Sample
- High, inflated whorls
- Very oblique mouth with thick lips
- Shell thicker than T. umbilicatum
- Surface markings more pronounced
- Greater separation of whorls in molds
Trochonema madisonense from the Arnheim Formation of Middletown, Ohio (OUIP 1134)
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Ulrich and Scofield (1897):
- A large shell agreeing in most particulars with T. umbilicatum, but having relatively higher and ventricose whorls, while the ridge, which generally surrounds the umbilical depression in this genus, is quite obsolete. The shell is thicker, the surface markings stronger, the mouth very oblique and with thicker lips. Casts of the interior of the two species are more alike than their exteriors, yet those of the present may be distinguished by the greater separation of the whorls due to the removal of a greater thickness of shell. There is a wide notch in the outer and upper portions of the peritreme which, with the somewhat triangular form of the aperture in a ventral view, suggests relations with T. eccentricum. Figures of that shell are given on the same plate with those of this species, so it is scarcely necessary to compare them further.