FIGURES 34–39 in Cyclotella petenensis and Cyclotella cassandrae, two new fossil diatoms from Pleistocene sediments of Lake Petén-Itzá, Guatemala, Central America

FIGURES 34–39. Type material of fossil lacustrine diatom Cyclotella cassandrae from lake Peten Itza, SEM. (34) Internal view of the valve margin along the major axis, MFP consisting of a short tube surrounded by three cowlings and located just at the tip of the costa below the marginal lamina. (35) Internal view of the valve margin along the minor axis where MFP are rather embedded in the costae at some distance of the marginal lamina and with triangular-shaped inserted costae. (36) Oblique internal view of a broken valve showing MFP on nearly each costae, a single short costa-born RM and CFP consisting of a tube with two to three cowlings scattered indifferently on the convex and concave part of the central area. (37) Born on a costa, a detailed view of the RM consisting of a shortly stalked labium with a radially orientated slit. (38) External view of a complete corroded frustule where the two valves are attached by an open valvocopula (black arrowhead) and fragments of collapsed and eroded girdle bands. (39) Internal view of a valve with a large fragment of a stepped valvocopula, a broken RM (black arrowhead) and CFP consisting of one tube with two or three cowlings. Scale = 10μm (38–39), 2μm (36), 1μm (34–35), 500 nm (37). Abbreviations: central fultoportulae (CFP), marginal fultoportulae (MFP), rimoportula (RM).