Pandora eocapsella, Carole & Hickman & Ca, 2014

Carole, Hickman, S. & Ca, 2014, Paleogene marine bivalves of the deep-water Keasey Formation in Oregon, part IV: The anomalodesmatans, PaleoBios 31 (3), pp. 1-21 : 6-7

Pandora eocapsella n. sp.

Fig. 1A

Diagnosis —Shell strongly compressed and strongly inequilateral; right valve shallowly concave, fitting inside shallowly convex left valve and apparently overlapped by left valve along posterioventral margin; anteriodorsal margin short and straight, posteriodorsal margin long, shallowly arcuate and thickened along hingeline; no evidence in preserved shell material of radial ribbing or co-marginal striae.

Description— Exterior shell layer missing but inner layers of sheet nacre well preserved; hinge plate insufficiently preserved to describe hinge teeth except for a tubercular swelling of nacre in position where right cardinal would have been.

Discussion— Although the exterior shell layer is not preserved in any of the Paleogene species, specimens are typically double valved and preserve distinctive details of shell shape. Evidence of co-marginal and radial sculpture are preserved in the interior nacre. Previous figures of specimens coated with ammonium chloride mask the taphonomic features that make shells so distinctive. This is illustrated in new, uncoated images of the holotype of P. acutirostrata Clark, 1918 from the San Ramon Formation (Oligocene) of California ( Fig. 1C) and the holotype of P. vanwinkleae Tegland from the Type Blakeley Formation (Oligocene) of Washington ( Fig. 1B). The Blakeley specimen demonstrates clear preservation of both co-marginal ribs and wavy axials characteristic of Pandorella Conrad, 1863. Articulated Holocene specimens of high latitude pandorids commonly show extensive exfoliation of the thin exterior shell layer. Differing degrees of degradation and exfoliation on live collected shells of Pandora trilineata Say, 1822 from Massachusetts ( Figs. 1D–F) illustrate how fossil shells can appear to be poorly preserved even if they have undergone little post-mortem alteration.

Etymology— Eo (Eocene, early) + capsella (a small box)

Material examined— The new species is known from a single specimen.

Holotype — UCMP 110671 , right valve with margins of larger left valve visible, Length 11.0 mm, height 9.5 mm, Loc. UCMP IP7983 (= USGS 25026 ).

Keasey Formation occurrence— Lower member in association with protobranch bivalves.