Tremalithus oamaruensis Deflandre in Deflandre & Fert, 1954
Valid according to ICN Art. 45 because originally described using ICZN codes. The Code used by Deflandre in Deflandre & Fert (1954) is determined "through internal evidence, irrespective of any claim by the author as to the group of organisms to which the taxon is assigned".
Elliptical placolith has a single cycle distal shield and a double cycle proximal shield. A disjunct diagonal crossbar with median lines spans the central area. The broad inner tube cycle and very narrow outer tube cycle impinges on the distal shield distally. The tube cycles, proximal shield and diagonal crossbars are birefringent in cross polarised light.
Chiasmolithus differs from Sullivania Varol (1992) by having diagonal crossbars with median sutures and double tube cycles visible distally. Chiasmolithus is distinguished from Cruciplacolithus Hay & Mohler in Hay et al. (1967) by having diagonal crossbars instead of axial crossbars. Moreover, a distally double tube cycle is visible in Chiasmolithus, whereas a single tube cycle is visible in Cruciplacolithus. Chiasmolithus are identified based on overall size, development of teeth like structure, size of the central area, and most importantly, arrangement of the diagonal central cross.
Deflandre, G. & Fert, C., (1954): Observations sur les coccolithophoridés actuels et fossiles en microscopie ordinaire et électronique. - Annales de Paléontologie. 40: 115-176.
Hay, W. W., Mohler, H. P., Roth, P. H., Schmidt, R. R. & Boudreaux, J. E., (1967): Calcareous nannoplankton zonation of the Cenozoic of the Gulf Coast and Caribbean-Antillean area, and transoceanic correlation. - Transactions of the Gulf-Coast Association of Geological Societies. 17: 428-480
Hay, W. W., Mohler, H. P. & Wade, M. E., (1966): Calcareous nannofossils from Nal'chik (northwest Caucasus). - Eclogae Geologicae Helvetiae. 59: 379-399.
Varol, O., (1992): Sullivania a new genus of Palaeogene coccoliths. - Journal of Micropalaeontology. 11: 141-150.