Tortolithus caistorensis Crux in Crux et al., 1982
Loxolith has a birefringent single protolith wall and a central area closed by overlapping plates.
Crux, J. A., Hamilton, G. B., Lord, A. R., Taylor, R. J., 1982. Tortolithus gen. nov. Crux and new combinations of Mesozoic calcareous nannofossils from England. INA Newsletter 4, 98-101.