Allonychia

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1872 Megambonia Meek, Proc. Acad. Nat. Sci., Philadelphia, p. 321.

1893 Allonychia Ulrich, Geol. Surv. Ohio, 7, p. 640.

1908 Allonychia Cumings, 32d Ann. Rep., Dep. Geol. Nat. Res. Indiana, p. 9678.

1909 Allonychia Grabau and Shimer, N.A. Index Fossils, 1, p. 432.

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Treatise on Invertebrate Paleontology, Part N, Vol. 1 of 3 (1969):

• With prominent anterior lobe; ornamented with simple, coarse, radial costae; without posterior wing or discernible byssal gape; hinge unknown.

Ulrich (1893):

• Shell containing a large size, a little obliquely subovate in outline, strongly convex, most gibbous somewhat above and in front of the middle, but with the point of greatest convexity situated further behind the anterior extremity than in any of the other genera of this family; beaks large, tumid, incurved, not terminal. Hinge line short, not alated posteriorly; just beneath the beaks a more or less well-defined, lobe-like protuberance of the anterior side, contains the byssal opening and usually forms the most anterior part of the shell. Surface radially costate. Hinge short, apparently edentulous, ligamental area high; posterior adductor scar large, deeply sinnate above, situated somewhat behind the middle of the valves; pallial line simple, extending up the anterior side to the umbonal cavity.

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