Actinogonium septenarium from Springfield, Barbados. Single example, along with two disc diatoms (look like Endictya sp.). Dipping down away from the coverslip towards the left hand side. Slight yellowing of the mountant. Prepared by William Allott Firth. Olympus BHB microscope using 450nm LED light. As well as the arrangement I imaged it with the 63x Leitz Pl Apo 1.4 objective, oil immersion. Olympus Aplanat Achromat condenser, oil immersion, oblique lighting. 2.5x Nikon CF PL photoeyepiece. Monochrome converted Nikon d850 camera. 44 images stacked in Zerene (Pmax).
Actinogonium septenarium Ehrenberg, 1847. Published in: Ehrenberg, C.G. (1847). Über die mikroskopischen kieselschaligen polycystinen als mächtige gebirgsmasse von Barbados und über das verhältniss der aus mehr als 300 neuen arten bestehenden ganz eigenthümlichen formengruppe jener felsmasse zu den jetzt lebenden thieren und zur kriedelbildung. Aine neue anregung zur erforschung des erdlebens. Ber. Verh. K. preuss. Akad. Wiss 1847: 40-60, 1 pl., 1 table. Page 54.
What is often referred to as Liostephania. For more discussion on what these might be, see here.