ABSTRACT

Meridionally costellate hedbergellids have been described from the upper Albian-Cenomanian of Libya (Hedbergella libyca Barr, 1972), the Cenomanian of Lebanon (H. costellata Saint-Marc), and the middle-upper Albian of the southeastern Atlantic, Deep Sea Drilling Project, Leg 40, sites 363 and 364. Meridional costellation was reported for a wide range of taxa at sites 363 and 364, leading to interference of a strongly ecophenotypic nature for meridional costellation. Definitions of costellate species have led to comparison with a large number of preexisting species and considerable taxonomic disorder.

Meridionally ornamented hedbergellids were encountered in samples from the upper Albian into lower Cenomanian of Deep Sea Drilling Project, Leg 43, site 386 in the western Atlantic (Bermuda Rise). The ornaments of spines, pustules, costellae, and meridionally oriented costellae are gradational into one another. Apertural properties are unstable and vary from typically hedbergellid to ticinellid. Emphasis on meridional costellation and instability of aperture has resulted in recognition of two, presumably ecophenotypic, forms of Hedbergella libyca, and the bringing together of several forms that had been scattered, largely by emphasis upon apertural features and taxonomic insignificance of meridional costellation.

Acceptance of H. libyca as described permits its separation from many previously suggested relatives and simplification of taxonomy. It also leaves H. libyca associated with the middle Albian into middle Cenomanian, a much narrower range of biostratigraphic value.

The sapropelic and related sediments in which the florid ornamentation of sites 363, 364 and 386 occurs imply extremities of physical environment of ample cause for ecophenotypic variation.