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Calocycletta costata (Riedel and Sanfilippo, 1959)

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Calocyclas costata Riedel, new species
Plate 2, figure 9

Description: Cephalis ovate, lobed, with sparse subcircular to circular pores and bearing a stout, conical apical horn. Thorax subspherical, with pores circular, hexagonally arranged and with a pronounced tendency to longitudinal alignment, the longitudinal rows separated by pronounced costae. No lumbar stricture externally. Abdomen subcylindrical or tapering distally, narrower than the widest part of the thorax. Abdominal pores subcircular or circular, arranged hexagonally with apparent longitudinal alignment (these longitudinal lines are continuous with those of the thorax) and often with longitudinal ridges separating pore rows.
Terminal feet eleven to eighteen in number, lamellar, usually truncate, parallel or slightly convergent, broader than the spaces between them, usually situated opposite alternate rows of abdominal pores. This species is distinguished from Calocyclas virginis by the pronouncedly costate thorax and otherwise smooth shell surface.

Dimensions (based on thirty specimens): Length of apical horn 115-230μm; of cephalis 30-45μm; of thorax 70-100μm; of abdomen 10-33μm; of feet 12-70μm. Breadth of cephalis 38-53μm; of thorax 103-135μm; of abdomen (distally) 75-108μm.

Localities and stratigraphic range: Challenger Sta. 225; Challenger Sta. 268; Chubasco core 9, 96-98 cm.; Chubasco core 40, 16-20 cm.; Swed. D.-S. Exped. core 91, 409-410 cm.; Globorotalia fohsi barisanensis zone (locality of the holotype, U.S.N.M. no. 563372) and Globigerinatella insueta zone of the Cipero formation, Trinidad.

This species has been found only in sediments from that part of the Lower Miocene corresponding approximately to Bolli's Globorotalia fohsi barisanensis and Globigerinatella insueta zones. Remarks: Although rare specimens appear to be transitional between Calocyclas virginis and Calocyclas costala, it is now considered advisable to recognize the two as distinct species. Transitional forms are to be expected if Calocyclas costata arose from Calocyclas virginis, as appears to have been the case.
Riedel and Sanfilippo 1959











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