Podocyrtis (Lampterium) fasciolata Nigrini

Podocyrtis (Podocyrtis) ampla fasciolata Nigrini, 1974, p.1069, pl.1K, figs.1-2, pl.4, figs.2-3

Podocyrtis (Lampterium) fasciolata Nigrini, Sanfilippo et al., 1985, p.697, fig.30.7

DESCRIPTION

Shell thick-walled, smooth. Cephalis subspherical with numerous subcircular pores, bearing a short, 3-bladed apical horn approximately the same length as the cephalis. Thorax campanulate to almost conical with subcircular pores aligned longitudinally (4 to 7 in a row) and distinct ridges between the pore rows; six to eight pores on a half-equator. Lumbar stricture distinct. Abdomen inflated, wider than thorax at its maximum breadth, narrows distally. Subcircular pores, larger than thoracic pores, usually aligned longitudinally (3 to 7 in a row) but sometimes irregular; six to eight on a half-equator. Wide poreless peristome usually with a smooth termination, but may show some thickening indicative of incipient feet. Rarely, three spathulate feet present (Nigrini, 1974).

DIMENSIONS

Based on 20 specimens from the Indian Ocean. Thorax 50-83 m long, 65-100 m wide (usually 83-100 m). Abdomen 83-150 m long, 115-165 m wide (Nigrini, 1974).

DISTINGUISHING CHARACTERS

P. (L.) fasciolata differs from P. (L.) sinuosa in not having the pronounced abdominal ribs and well developed shovel-shaped feet of the latter. From P. (Podocyrtoges) ampla it differs in its smaller size - total length (excluding horn) 165-250 m (usually 200-230 m); maximum width of abdomen 105-175 m (usually 115-160 m); thoracic length 80-100 m - and shorter horn commonly bladed (Sanfilippo et al., 1985).

Measurements given by Sanfilippo et al., 1985 show a broader range than those reported by Nigrini (1974). Probably this is because Nigrini was measuring only Indian Ocean material whereas Sanfilippo et al. included material from the Pacific, Atlantic and Caribbean and from a longer stratigraphic range.

VARIABILITY

The campanulate to conical thorax has pores aligned in longitudinal rows and separated by more or less pronounced ridges. Lumbar stricture moderately distinct. The inflated abdomen has large pores of variable size (6-10 pores on a half-equator), sometimes irregularly arranged and sometimes in longitudinal rows with very vague ridges between them. These pores, in well preserved specimens, tend to be subdivided by an internal, fine, irregular meshwork. When the pores are irregularly arranged, the outline of the abdomen is rough. The wide, pore less peristome is usually smooth and thick, but may rarely have indications of three spathulate feet (Sanfilippo et al., 1985).

DISTRIBUTION

P. (L.) fasciolata has a short range in the middle middle Eocene and has been found in the Gulf of Aden at DSDP Pacific Site 40, in the Gulf of Mexico and in the Caribbean. Its morphotypic first appearance lies within the Podocyrtis ampla Zone. Its morphotypic last appearance lies within the Podocyrtis mitra Zone.

PHYLOGENY

Instead of being a geographic variant of P. (Podocyrtoges) ampla (Nigrini, 1974, p.1069), this form is now considered to be an off-shoot of the lineage from P. (L.) sinuosa to P. (L.) mitra. For this reason it is elevated to species rank and placed in the subgenus Podocyrtis (Lampterium). At the time of its acme, P. (L.) fasciolata far outnumbers the co-occurring P. (L.) sinuosa.

REMARKS

Additional illustrations can be found in Riedel and Sanfilippo, 1973, pl.4, figs.1-3.

For generic level taxonomy see Sanfilippo and Riedel, 1992.

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