SEM images of rostroconch shells Mokshatuba okaensis (Pseudobigaleaidae) from the Pennsylvanian of the Russian Platform. VEGA3 TESCAN scanning electron microscope at the Paleontological Institute of the Russian Academy of Sciences, Moscow.

Figure 3. Mokshatuba okaensis gen. et sp. nov., Holotype 4471/85-245, Akulshino quarry; Korobcheevo Formation; 12×.(A–F) Latex cast of the external surface of the outer shell layer: ventral (A), dorsal (B), oblique ventral (C), posterior (D), right lateral (E), and anterior (F) views. (G) Line drawing based on Fig. F, showing zones of the anterior part of the shell (dotted lines indicate zones of the external surface of the inner shell layer not visible on the specimen). (H) Internal mold (steinkern), anterior view. (I) Drawing with reconstruction based on Fig. H. Abbreviations: sn — snout; fs — frontal segment; co — collum area; cb — central body; hd — hood; rr — radial rib; arr — additional radial rib; rc — rostral cleft. Figure 4. Mokshatuba okaensis gen. et sp. nov., paratype PIN 4471/85-246, Akulshino quarry; Korobcheevo Formation; 12×. (A–D) Steinkern: oblique ventral (A), left lateral (B), dorsal (C), and anterior (D) views. (E–H) Latex cast of the external surface of the inner shell layer: anterior (E), dorsal (F), oblique ventral (G), and right lateral (H) views. Abbreviations: lu — lunulazone; vo — ventral orifice; vc — ventral commissure; ds — cast of dorsal longitudinal septa; cc — internal mold of conical cavity. Figure 5. Mokshatuba okaensis gen. et sp. nov., Akishino quarry; Korobcheevo Formation; 12×. (A–G) Paratype PIN 4471/85-248: (A–F) Latex cast of the external surface of the inner shell layer: right lateral (A, B), dorsal (C), oblique ventral (D, F), and anterior (E) views. (G) Internal mold (steinkern), anterior view. (H, I) Paratype PIN 4471/85-247: Latex cast of the external surface of the inner shell layer and fragments of the outer layer: ventral (H) and left lateral (I) views. (J) Sketch of the boundary (white line) between the outer and inner shell layers, anterior part of the shell. (K) Sketch of the boundary (white line) between the outer and inner shell layers, posterior part of the shell. Abbreviations: lu — lunulazone; vo — ventral orifice; rra — radial ribs of rostral area; sol — external surface of the outer shell layer; sil — external surface of the inner shell layer; fs — frontal segment; co — collum area; vs — ventral segment; ra — rostral area; ol — outer shell layer; il — inner shell layer.