Lower-Middle Devonian conodonts (serotinus-kockelianus zones) from the Třebotov Limestone (Daleje-Třebotov Formation) and Choteč Limestone (Choteč Formation) were studied. The following sections in the Prague Basin were sampled in an attempt to refine the conodont biostratigraphy of this sequence: Barrandov road cut, Prastav quarry at Holyně, Jelínek mill quarry at Chýnice and Červený quarry near Suchomasty. Another aim was to collect new data from sections which have not been sampled before: Na Škrábku quarry at Choteč, U Němců section at Karlštejn and Na vyhlídce section at Hostím. The main focus was on clarifying ranges of individual conodont taxa and thus enabling more precise correlations to be made.

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A systematic study of Silurian and Devonian platyceratid gastropods provides new data on their early shell ontogeny. Typical cyrtoneritimorph protoconchs were found in <i>Praenatica cheloti </i>(Oehlert & Oehlert, 1887) from the Lower Devonian strata of Brittany (W France). The same protoconch type, as in <i>Praenatica</i> Barrande in Perner, 1903, was earlier documented in <i>Orthonychia </i>Hall, 1843. Both of the latter taxa have often been considered to be subgenera of <i>Platyceras</i> Conrad, 1840. However, Silurian and Devonian species of <i>Platyceras</i> from the Barrandian area develop quite different protoconchs (orthostrophic and tightly coiled), similar to those found earlier in different species of the family Naticopsidae Waagen, 1880. Current data suggests that Paleozoic platyceratids represent a diphyletic group. The nature of their protoconchs (development of a true larval shell) testifies against the hypothesis that the Paleozoic platyceratids are the stem group for the Patellogastropoda. However, the derivation of modern neritimorphs from Paleozoic “platyceratids” with tightly coiled protoconchs or from the naticopsids seems to be probable. The strongly convolute neritimorph protoconch (apomorphy of neritimorph crown-group) probably originated after the Permian/Triassic mass extinction event, but before the Late Triassic