. Bulletin of the Natural Histort Museum. Geology series. 32 POPOV. COCKS AND NIKITIN 1() 2(). 16() 10 I 20 mm j i Fig. 10 Transverse serial sections of conjoined valves of Teratelasmella chugaevae sp. nov. from Sample 100. Distance in mm is measured from the posterior tip of ventral beak. Dorsal valve uppermost. Also lateral view to show section positions and schematic reconstruction. 90% as thick as long. Anterior commissure strongly uniplicate. Ventral valve moderately convex with maximum thickness near quarter valve length. Interarea high, triangular, apsacline wi
. Bulletin of the Natural Histort Museum. Geology series. 32 POPOV. COCKS AND NIKITIN 1() 2(). 16() 10 I 20 mm j i Fig. 10 Transverse serial sections of conjoined valves of Teratelasmella chugaevae sp. nov. from Sample 100. Distance in mm is measured from the posterior tip of ventral beak. Dorsal valve uppermost. Also lateral view to show section positions and schematic reconstruction. 90% as thick as long. Anterior commissure strongly uniplicate. Ventral valve moderately convex with maximum thickness near quarter valve length. Interarea high, triangular, apsacline with delthyrium completely covered by pseudodeltidium perforated by a small umbonal foramen. Ventral sulcus originating at the umbonal area, strongly deepening anteriorly and ending with prominent, semielliptical tongue inclined at less than a right angle to the com- missural plane. Flanks of the valve flattened, slightly inclined to the commissural plane. Dorsal valve very strongly convex, with a low, anacline interarea. Strong median fold, rounded in cross-section, with steep lateral slopes originating near the beak. Very weak and narrow dorsal median sulcus in the umbonal area of some specimens. Radial ornament coarsely parvicostellate with 5 ribs per 3 mm along the posterior margin of mature specimens. Interiors of both valves were studied in transverse sections (Figs 10, 11). Ventral valve with strong teeth supported by high dental plates continuing anteriorly as muscle bounding ridges. Low median ridge in the anterior half of the ventral muscle field. Dorsal valve interior with bilobed cardinal process and low, curved socket ridges. Median septum high, triangular, blade-like, extending anteriorly to mid-valve, flanked laterally by a pair of short side septa. Adductor field raised anteriorly and bordered by a high rim. DISCUSSION. This species is similar only to Teratelasmella plicata Laurie, 1991. but it can be distinguished in being larger (up to mm wide), with a stro
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