Pterocorys campanula Haeckel, 1887, p.1316, pl.71, fig.3; Caulet and Nigrini, 1988, p.226, pl.1, figs.2-5 (with synonymy)
Shell conical to ovate, thin-walled, smooth except for longitudinal ridges at irregular intervals on the thorax. Rarely, there is a single ridge, which is prolonged into the abdominal wall. Cephalis trilocular with numerous subcircular pores. Stout three-bladed apical horn about the same length as of a little longer than the cephalis. Primary lateral and dorsal spines aligned with three ribs in the thoracic wall.
Thorax inflated conical with subcircular to circular pores arranged in longitudinal rows, ornamented by irregular longitudinal ridges. In some specimens thoracic ribs project as small thorns or triangular, pored wings. Lumbar stricture distinct.
In Pacific Ocean sediments, early forms have a much inflated abdomen (> 120 µm), broader than the thorax, but with similar pores. In later specimens the abdomen is less inflated (< 120 µm), more cylindrical. In Indian Ocean sediments early forms have a rather narrow abdomen (< 120 µm) and later forms are more inflated (> 120 µm). Termination always ragged (Caulet and Nigrini, 1988).
Total length (excluding apical horn) 139-217 µm. Length of apical horn 28-43 µm; of cephalis 26-37 µm; of thorax 48-68 µm; of abdomen 77-115 µm. Maximum breadth of cephalis 24-29 µm; of thorax 90-110 µm; of abdomen 110-140 µm (Caulet and Nigrini, 1988).
More than three longitudinal ridges on the thorax; very rarely a single ridge projects into the upper part of the abdomen (Caulet and Nigrini, 1988).
We have been able to observe the intermediate form in which a single rib continues for a short distance into the abdomen. Initially we consider this form to be a P. campanula, but we now record it separately as an unnamed transitional form (Caulet et al., 1993).
Common in both tropical Indian and tropical Pacific Ocean sediments. Its morphotypic first appearance lies within the Stichocorys peregrina Zone and its morphotypic last appearance is a synchronous event that lies within the Amphirhopalum ypsilon Zone.
Evolved from P. clausus (see Caulet and Nigrini, 1988, p.229) during the lowermost Pliocene. Ancestor of Pterocorys hertwigii.