A hyaline flap of silica forming a cavity on the external valve face, lying along the apical axis. Proximal edge, or edge near the raphe, arises a distance from the raphe. Distal edge joins the valve near the valve margin. Cavity formed by the pseudoconopeum is open at both ends. Striae on the floor of the cavity have fewer areolae than striae outside the pseudoconopeum. Areolae or other ornamentation are present between the pseudoconopeum and the raphe. Found only in some marine species of the genus Mastogloia.
By contrast, the proximal margin of a true conopeum forms the edge of the raphe slit. Compared to lateral sterna, pseudoconopea do not join at the central nodule.
Paddock, T.B.B. and Kemp, K.D. (1990). An illustrated survey of the morphological features of the diatom genus Mastogloia. Diatom Research 5: 73-103.