. Bulletin of the Natural Histort Museum. Geology series. 66 POPOV, COCKS AND NIKITIN. Fig. 15 Photographs of transverse serial sections, x 12. Distance in mm is measured from the posterior tip of ventral beak. Dorsal valve uppermost. 1-2, Placotriplesia spissa , BC 57605, Sample 628, Kujandysai section; 1, mm; 2, mm. 3,4, 9-14, Ilistrophina tesikensis gen. et sp. nov., Sample 948, Tesik River, 3,4, BC 57606, and mm; 9-14, BC 57607, , , , and mm; 5-7, Parastrophina iliana sp. nov., BC 56560, Sample 948, Tesik River; , and mm;
. Bulletin of the Natural Histort Museum. Geology series. 66 POPOV, COCKS AND NIKITIN. Fig. 15 Photographs of transverse serial sections, x 12. Distance in mm is measured from the posterior tip of ventral beak. Dorsal valve uppermost. 1-2, Placotriplesia spissa , BC 57605, Sample 628, Kujandysai section; 1, mm; 2, mm. 3,4, 9-14, Ilistrophina tesikensis gen. et sp. nov., Sample 948, Tesik River, 3,4, BC 57606, and mm; 9-14, BC 57607, , , , and mm; 5-7, Parastrophina iliana sp. nov., BC 56560, Sample 948, Tesik River; , and mm; 8, Parastrophina plena Sapelnikov & Rukavishnikova, BC 57564. Sample 948. Tesik River, mm. about 66% valve width. Dorsal valve strongly convex with maxi- mum thickness at mid-valve or slightly anteriorly. Umbonal area strongly swollen. Broad median fold originating near mid-valve. Radial ornament of coarse rounded-angular ribs originating anterior to mid-valve in mature specimens with 1-3 ribs in the sulcus, 2-4- on the median fold and up to 6 on the flanks of both valves. Ventral interior with small teeth and narrow spondylium on a low median septum extending anteriorly to mid-valve. Dorsal interior with narrow cruralium on the low median septum. Alate plates small, projecting anteriorly as short brachial processes. Inner plates narrow, gently curved. Outer plates nearly straight in cross-section, converg- ing towards a thin median septum. Measurements. (471/12375) conjoined valves, L= , W=l , T=, Sw=; (474/12375) conjoined valves, L=, W=, T=, Sw=; (475/12375) conjoined valves, L=, W=, T=, Sw=; (476/12375) conjoined valves, L=, W=, T=, Sw=; (479/12375) conjoined valves, L=, T=, Sw= Discussion. The Kazakh shells are comparable to Parastrophina haemiplicata (Hall), and in particular with specimens described and illustrated by Cooper (1956: 606, pi. 106, figs 33^14; pi. 117, figs 19-27) from the lower M
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