A thin siliceous covering over the striae on the external valve surface. The conopeum may be slightly to distinctly elevated from the valve face. The width of conopea is variable, but may extending to the valve margin. This structure is visible with scanning electron microscope. Conopea have been found to contain symbiotic nitrogen-fixing cyanobacteria and are found in a number of genera, including Fallacia, Lyrella, Microcostatus and Sellaphora.
Barber, H.G. and Hayworth, E.Y. (1981). Guide to the Morphology of the Diatom Frustule. Freshwater Biological Association, 112 pp.