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Artophormis cf. gracilis Riedel, 1959

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Antarctic form similar to A. gracilis but which lacks distinct ribs in the fourth segment.

Artophormis gracilis
Description: Shell conical above, subcylindrical below, consisting of four segments separated by moderately distinct strictures. Cephalis globular, hyaline or with a few small pores, bearing an apical spine, which may be simple conical, multiple, or latticed. Thorax truncate-conical and abdomen inflated annular, both of these segments rather thick-walled, with rough surface and pores subcircular or circular, irregular in size and arrangement. Fourth segment consisting essentially of four to twenty longitudinal ribs joined together by a rather delicate lamellar meshwork with irregular pores; the longitudinal ribs terminate in free spines, and in some specimens are not clearly distinguishable from the meshwork.
This species differs from Artophormis barbadensis (Ehrenberg, 1874, pp. 217-218; 1876, pi. 18, fig. 8: Haeckel, 1887, p. 1459), which occurs in the Eocene part ofthe Oceanic formation of Barbados, in having a more inflated third segment, and in the greater differentiation of the fourth segment from the third.
Dimensions (based on thirty specimens): Length of apical horn 3-63; of cephalis 20-30; of thorax 38-58 of abdomen 43-78; of fourth segment (including terminal spines) 25-145. Maximum breadth (at third or fourth segment) 95-145.
Localities and stratigraphic range: Chubasco core 17, 11-15 cm. (locality of the holotype, U. S. N. M. no. 563375); Chubasco core 38, 11-15 cm.; Downwind core BG 10, 13-15 cm.; MidPac core 5-1, 26-27 cm.; "Bath Schichten," Oceanic formation, Bath, Barbados.
This species apparently ranges from the Lower Oligocene to the lowermost Miocene.

Riedel 1959


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