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Three species of isolated Upper Jurassic Calcisphaerulidae have previously been described from the Indian Ocean DSDP Leg 27, Site 261, situated in the northeastern Argo Abyssal Plain (Bolli, 1974): Pithonella carteri, P. mcnightii, and P. thayeri; P. carteri is a spherical form from the Tithonian whose single-layered test consists of fairly tightly packed, mostly elongate, very small calcite crystals. P. mcnightii is also a single layered Tithonian spherical form but has distinctly larger, loosely packed irregularly arranged tabular and angular crystals separated by interspaces. The single-layered test of the third species, P. thayeri, consists of very large, irregularly shaped crystals. P. thayeri has been found in upper Oxfordian to Tithonian sediments. The two species here described as Bonetocardiella paulaworstellae n. sp. and B'. williambensonii n. sp. are about the same age and come from the Upper Jurassic sediments of Hole 391C. They bear some resemblance to P. carteri and P. mcnightii from Site 361. B. paulaworstellae has a similarly fine-grained outer layer similar to that of P. carteri. B. williambensonii is characterized by large tabular crystals loosely and irregularly arranged, similar to those of P. mcnightii (see Figure 1). A number of features present in these newly described species from Hole 391C, however, clearly distinguish them from the Indian Ocean forms. The test shape in particular is not fully spherical, but is distinctly flattened and depressed around the apertural area forming a slightly cupped sphere. The aperture consequently lies in a depression, like that characterizing the genus Bonetocardiella. Because of this feature the two new species are here tentatively included in the genus Bonetocardiella, even though the test outline does not resemble the heart-shaped peripheral outline typical for the genus. An alternative would be to place the species on the basis of its nearly spherical shape in the genus Pithonella. Representatives of Bonetocardiella have not previously been found in sediments older than Albian. A link would still have to be found to establish that the forms described here are generically related to the Albian and Late Cretaceous Bonetocardiella.

Upper Jurassic Calcisphaerulidae from DSDP Leg 44, Hole 391C, Blake-Bahama Basin, Western North Atlantic