Bairdoppilata martyni Coryell, Sample and Jennings 1935

Bairdoppilata martyni Coryell, Sample and Jennings, 1935

(Figures 15J–L)

1935 Bairdoppilata martyni Coryell, Sample and Jennings: 3, text-figs. 1, 2.

? 1942 Bairdoppilata cf. B. martyni Coryell, Sample and Jennings. —Vernon, p. 60–66.

?1964 Bairdoppilata margini [sic] Coryell, Sample and Jennings.—Puri & Vernon, p. 114.

1974 Bairdoppilata martyni Coryell, Sample and Jennings. —Poag, p. 346.

Material Examined: Several fossil valves (including RV specimen 1018 RV, LV specimen 1019LV) in UH 0083, collected from the type locality.

Dimensions: LV specimen 1019LV: LVL 1.057 mm, LVH 0.675 mm; RV specimen 1018RV: RVL 1.060 mm, RVH 0.647mm. Coryell, Sample & Jennings (1935) reported carapace length 1.030 mm, carapace height 0.68 mm.

Anatomical Remarks. The valves are smooth, lacking puncta. In lateral outline the LV is rounded-subtriangular, with the greatest height being located at about one-third of length (Fig. 16L). The posterior angle is located rather low, at about one-quarter of height. Supplemental dentition is well developed in these specimens. Nothing is known of the flapper valve or other soft anatomy in this fossil species.

A distinctive patch pattern is preserved (Figs. 15J–L), which does not resemble any modern species of the Gulf Coast and Caribbean. It features a shield-shaped, central opaque spot, which is connected by three or more narrow bridges to a broad opaque expanse covering the dorsal margin and the posterior region. Numerous clear, circular islands are located within this posterior opaque region. A familiar spot is present at the anterior corner, but the crescentic vertical streak in the central-anterior region has no analogue among the living Caribbean species.

Taxonomic Remarks: Photographs of topotype specimens of this species are offered here, to supplement the drawings that accompanied the original published description.

Howe & Law (1936, p. 28) compared their new species B. taxodonta to B. martyni, stating: “The closely related B. martyni of the Lower Chickasawhay may not be separated easily from B. taxodonta in exterior view, but from the interior it shows a more delicate carapace with thinner, narrower margins and a more delicate hinge. Translucent specimens usually show three vertical cloudy areas instead of one, and the inner edge of the hinge line is decidedly angulate instead of being broadly rounded.”

Poag (1974) reported that B. martyni occurs consistently but in low numbers at six exposures of the Chickasawhay Formation and the overlying Paynes Hammock Formation, in southeastern Mississippi and Alabama. These units belong to the Chickasawhayan Local Stage of early Late Oligocene age. He did not find it in the underlying Byram Marl and Bucatunna Formations. The species has also been reported from the Suwannee Limestone of the Florida Panhandle (Vernon 1942, Puri & Vernon 1964).