Anorthoneis hummii Hustedt 1955: 15

Anorthoneis hummii Hustedt 1955: 15 ( Figs 49–67 View FIGURES 49–56 View FIGURES 57–62 View FIGURES 63-67 )

References:— Hustedt (1955), p. 15, pl. 2 fig. 6, pl. 5 figs 18–19; Simonsen (1987), p. 405, pl. 605, figs 1–9; Witkowski et al. (2000), p. 97, pl. 42, fig. 22.

Description. Valves outline varies from ovoid to roundish ( Figs 57 View FIGURES 57–62 , 63 View FIGURES 63-67 ). Apical axis: 27–41 μm; transapical axis: 23–36 μm.

SV:— Externally, valve face flat to convex, curving abruptly into a shallow, imperforate mantle ( Fig. 58 and 60 View FIGURES 57–62 ). Sternum depressed, asymmetric, terminating in small roundish hyaline areas, close to the valve margin ( Fig. 57 View FIGURES 57–62 arrow). Central area not clearly defined ( Fig. 57 View FIGURES 57–62 ). Transapical striae uniseriate on both the valve face and the mantle, from 8 in 10 μm close to the margin to 10 in 10 μm close to the sternum, composed of large, transapically elongated areolae ( 10 in 10 μm). Thick hymenes occluding externally the areolae perforated by round porelli in a circular to regular scatter ( Fig. 59 View FIGURES 57–62 ). Internally, valve face concave, with raised narrow sternum, expanding laterally into large asymmetric roundish central area ( Fig. 62 View FIGURES 57–62 ). Mantle virgae visibly raised ( Fig. 61 View FIGURES 57–62 ).

RSV:— Externally, valve face almost flat to slightly concave, sloping gently into a shallow mantle ( Fig. 67 View FIGURES 63-67 ). Striae radial, uniseriate, becoming biseriate close to the valve margin, 20 in 10 μm ( Figs 65, 66 View FIGURES 63-67 ). Areolae large, roundish (valve face) or transapically-elongated (mantle), 30 in 10 μm, occluded by hymenes ultrastructurally similar to those in the SV ( Fig. 66 View FIGURES 63-67 ). Central area very narrow, not well discernible, flanked by imperforated small areolae ( Fig. 64 View FIGURES 63-67 ). Proximal raphe endings expanded, pore-like, coaxial and lying in concave drop-shaped area ( Fig. 64 View FIGURES 63-67 ). Distal raphe endings expanded, pore-like, hardly reaching hyaline submarginal areas ( Fig. 65 View FIGURES 63-67 , arrow), distant from the valve margin. Valvocopula open, with a smooth inner margin ( Figs 65 and 66 View FIGURES 63-67 ).