SYSTEMATIC PALEONTOLOGY

(by J.E. Arney, B. Ladner, and S.W. Wise Jr.)

Basionym: Cyclothlithus? robustus Bramlette & Sullivan, 1961, p. 141, pl. 2, fig. 7a-7c.

Remarks: Wei (1998) has provided an excellent and thorough discussion (with synonymy) of this taxon, which he assigns to the genus Ericsonia Black, 1961, following the example of Perch-Nielsen (1977). The species consists of three cycles of elements, not unlike those in some species of Heliolithus (e.g., H. universus Wind and Wise, 1977). In H. robustus, however, the three cycles are tightly appressed. One could argue that the middle cycle corresponds to the outer distal shield in the genus Coccolithus (= Ericsonia of authors) and therefore should not birefringe in cross-polarized light. Because each cycle in a given specimen of H. robustus reaches about the same outer diameter, however, we have not been able to demonstrate such an optical effect under crossed nicols. Instead, each cycle appears to be entirely birefringent, a characteristic that fits the definition of Heliolithus rather than Coccolithus or Ericsonia.