Grondboor & Hamer , Volume 48 - Issue 3 p. 54- 58
The author reports on the occurrence of Ordovician rostroconch mollusks in erratic pebbles and boulders, collected in Lower-Pleistocene fluvial sediments from the Saalian ice-pushed ridges in Twente (NE of The Netherlands) and the neighbouring westernmost part of Germany (County of Bentheim). In the Middle-Ordovician (Caradoc; Estonian stages C3-D2) silicified limestone (Backsteinkalk) 15 specimens of Ischyrinia sp., 2 other Ischyrinia-related rostroconchs and 2 Conocardium- or Hippocardia-like rostroconchs have been collected. specimens of Ischyrinia sp. are preserved as internal moulds and show part of the outer cast as well. In the Upper-Ordovician (Ashgill; Estonian stages F1c-F2) silicified Öjlemyrlimestone and -chert about 25 specimens have been found until now. One specimen could be Pinnocaris sp., all others are probably Conocardiidae and Hippocardiidae. Some specimens show magnificently parts of the hood, others very finely preserved lamellae-structures of the casts. Of some specimens the internal mould has been preserved as well. A few specimens of Hippocardia sp. are pressed together (Fig.3-6). To identify these fossils further investigation is necessary. All specimens but one (Fig. 1, 2) are in the author's private collection.
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