Delectopecten, Hickman, 2023

Hickman, Carole S., 2023, Paleogene marine bivalves of the deep-water Keasey Formation in Oregon, Part II: The pteriomorphs, PaleoBios 40 (5), pp. 1-51 : 30

DELECTOPECTEN N. SPP.

Fragmental specimens from two localities in the Keasey formation have forms of ornamentation that differ dramatically from the two species described above as well as from one another. The inferred maximum length and height of the specimens at hand is <1 cm. In both species the sculpture changes abruptly during ontogeny. The first is from the classic Mist locality ( USGS 15318 ) and is represented by an external mold ( USNM 561848 ) in which radial and concentric ribs of equal strength on the dorsal half of the disc cross one another to form a scaly pattern that changes abruptly to a very fine ra- dial camptonectes pattern that continues to the ventral shell margin. The second species is from a locality in the upper member ( USGS 15315 ) and is represented by an external mold with a different discrepant sculpture pattern. On this specimen the subumbonal portion of the disc is smooth, with an increasingly well-developed concentric sculpture on the dorsal portion changing abruptly to a relatively coarse cancellate pattern that continues to the ventral margin. Descriptions were never published, although Harold Vokes obtained the prospective USNM type numbers and intended to propose a new name for the upper Keasey specimens and to treat the Mist specimen in open nomenclature. The material is here considered inadequate for proposing new names. However , the distinctive sculptural patterns in these fragmental specimens call attention to the diversity in the Keasey mud pecten fauna. It is perhaps significant that the Mist specimen occurs at one of the three methane seep localities in the formation, co-occurring with the abundant propeamussiid species described below .