The paper describes a new member of a group of Lower Palaeozoic marine fossils which partly bridge the gap between echinoderms and chordates. Evidence suggests that this group included the ancestors of the vertebrates. Its members are traditionally regarded as primitive echinoderms, but are better seen as primitive chordates with echinoderm affinities. They form a basal subphylum of chordates-the Calcichordata Jefferies 1967. The Calcichordata, in accordance with an early suggestion by GislCn, are probably ancestral to all living chordates.The new calcichydate is named Reticu/ocarposvhanui gen et sp. nov. I t comes from the Lower Ordovician Sirka Formation (Llanvirn) of Sdrka near Prague, Czechoslovakia and is placed in the family Amygdalothecidae Ubaghs 1970. I t is important because of its position in the Calcichordata. This group is divided into two very different orders-the Cornuta and the Mitrata. The Cornuta are the more primitive order and gave rise to the Mitrata, which had the structure of giant, calcite-plated tunicate tadpoles. Many features show that the new species is a very advanced cornute, closely related to the stock that gave rise to the mitrates. For this reason it is important in the general history of the chordates, since some primitive mitrate was probably the latest common ancestor of the living chordate subphyla i.e. of tunicates, of amphioxus and its allies and of the vertebrates.Being a rnitrate-like cornute, the new species allows the cornutes and mitrates to be compared more confidently than before. Four results are especially important. Firstly it is likely that the stem (=tail) of mitrates is equivalent only to the anterior part of the stem of cornutes. This is significant, because traditional views as to which was the upper surface in rnitrates have been based on stem homologies now seen as false. Secondly Reticulocarpos hanusi is adapted to stay up on very soft mud, using only the strength of the mud for support. The mitrates, on the other hand, supported themselves on soft mud by a much more reliable method resembling buoyancy. Thirdly, the new form had paired transpharyngeal eyes which are otherwise known only in mitrates, and which are the earliest type of paired eyes in chordates. Fourthly, it becomes possible to homologize the thecal plates of cornutes with those of mitrates.Reticulocarpos hanusi represents an important phase in chordate evolution dominated by the necessity of staying up on mud by a very precarious method. During this phase many pre-adaptations for swimming were acquired. Primitive mitrates, descended from a very similar form, were probably the first chordates that could swim.V prici je popdn Reticulocarpus hanusi n. gen. n. sp., novL druh primitivnich chordhi z podkmene Calcichordata Jefferies, 1967. Calcichordata jevi blizkt vztahy k ostnokoicum a takt se jim do znaEnC miry podoba ji. Zahrnujeme do nich dva Tidy, Mitrata a Cornuta, ktert byly diive, spolu s dalgimi dv'ema Mdy, Soluta a Cincta fazeny do th'dy Carpoidea Jaekel, 1900. 6 9 7 0 R. P. S. JEFFERIES...

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In washings of weathered Třebotov Limestone of Early Devonian, Late Emsian age, isolated radials and rarely, the almost complete calyxes of new zophocrinid crinoids, have been found. These crinoids are closely related to the genus Tiaracrinus and are described here as a new genus and new species, Baficrinus vigilis gen. nov. et sp. nov. A list of crinoid taxa and parataxa described from the Třebotov Limestone in the Barrandian Area is included herein.

The paper represents the first ciritical list of hitherto described species of Bohemian Devonian crinoids, with determination of their correct stratigraphic ranges. The crinoid assemblages from single stratigraphic stages in the Bohemian Lower and Middle Devonian are characterized for the first time. The possibility of the determination of the Silurian-Devonian and Lower-Middle Devonian boundaries on the basis of crinoid faunas is discussed. Zusammenfassung. Es wird eine kritische U bersicht der stratigraphischen Verbreitung der bisher be schriebenen Krinoiden des bohmischen Devons gegeben. Die Krinoiden-Vergesellschaftungen in den stratigraphischen Stufen des bohmischen Unter-und Mitteldevons werden charakterisiert und Moglich keiten der Grenzziehung Silur-Devon sowie Unter-Mittel-Devon im Barrandium mit Hilfe der Krinoiden diskutiert.

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