The Devonian nautiloids Hercoceras Barrande, 1865 and Ptenoceras Hyatt, 1894 are closely related and should be classified within the single oncocerid family of Hercoceratidae Hyatt, 1884, which has priority before the family Ptenoceratidae Teichert, 1939. This is supported particularly by the similarity of their embryonic shell and by the character and ontogeny of ventrolateral outgrowths. The intraspecific variability of shells in Hercoceras mirum Barrande, 1865 (Lower Devonian, Prague Basin, Czech Republic) is striking and unusual among nautiloids. The variability in Ptenoceras alatum (Barrande, 1865) is also high, demonstrating fluent transitions between individual morphotypes. Therefore, the other two species of this genus described from the Pragian Stage of the Prague Basin, Ptenoceras modicum (Barrande, 1877) and Ptenoceras barrandei Zhuravleva, 1974 should be assigned to the single species Ptenoceras alatum. • Key words: Cephalopoda, Nautiloidea, taxonomy, variability, Lower Devonian, Prague Basin, Barrandian.

TUREK, V. 2007. Systematic position and variability of the Devonian nautiloids Hercoceras and Ptenoceras from the Prague Basin (Czech Republic). Bulletin of Geosciences 82(1), 1–10 (7 figures). Czech Geological Survey, Prague. ISSN 1214-1119. Manuscript received January 8, 2007; accepted in revised form February 13, 2007; issued March 30, 2007. • DOI 10.3140/bull.geosci.2007.01.1

Vojtìch Turek, National Museum, Department of Palaeontology, Václavské námìstí 68, 115 79 Praha 1, Czech Republic; vojtech_turek@nm.cz

Ordovician chitinozoans from Skane (Sweden) and Bornholm (Denmark), in southernmost Scandinavia, are discussed. Previously published information on Ordovician chitinozoans from these two provinces is reviewed and complemented with new data. Characteristic Baltoscandian chitinozoan faunas have been found from the uppermost Tremadocian (H. copiosus Zone) to the Ordovician–Silurian boundary interval. Besides the uppermost Tremadocian strata, the Lower Ordovician part of the Toyen Formation (Floian to lowermost Darriwilian) has not been investigated. The Belonechitina micracantha – robusta – wesenbergensis complex is discussed in some detail. The forty-nine species, of which twelve in open nomenclature, are from fifteen genera. One species, Conochitina scabra n. sp., from the uppermost Lindegard Mudstone and lower Tommarp Formation (uppermost Katian–lower Hirnantian) in Skane, is newly described. • Key words: Ordovician, Chitinozoa, Scandinavia, Skane, Bornholm.

GRAHN, Y. & NOLVAK, J. 2007. Ordovician Chitinozoa and biostratigraphy from Skane and Bornholm, southernmost Scandinavia – an overview and update. Bulletin of Geosciences 82(1), 11–26 (11 figures). Czech Geological Survey, Prague. ISSN 1214-1119. Manuscript received May 22, 2006; accepted in revised version November 29, 2006; issued March 30, 2007. • DOI 10.3140/bull.geosci.2007.01.11

Yngve Grahn, Universidade do Estado do Rio de Janeiro, Faculdade de Geologia, Bloco A – Sala 4001, Rua São Francisco Xavier 524, 20550-013 Rio de Janeiro, R.J., Brazil; yngvegrahn@hotmail.com • Jaak Nolvak, Tallinn University of Technology, Institute of Geology, Ehitajate tee 5, 19086 Tallinn, Estonia; nolvak@gi.ee

Our current studies of the exoskeletal structures and ultrastructures in Lower Devonian dalmanitid trilobites of the Prague Basin are briefly described and discussed. The interior of the exoskeleton in most specimens from the Prague Basin is recrystallised and largely filled with very fine homogeneous sparitic cement. The ultrastructures sensu stricto, e.g., the lamination, layers forming the exoskeleton, and the fine pores or “Osmólska” cavities, are mostly imperceptible even at higher magnifications. However, ultrastructural relics were observed in some polished thin sections and exoskeletal fragments using electron microscopy. Larger structures, especially the eyes, the megapores penetrating the exoskeleton, and the surface sculptures (prosopon sensu Gill 1949), are relatively well preserved and show very fine details. The biological significance of megapores is briefly discussed. Modification of the inner parts of the exoskeletons by diagenetic processes, obscuring most of the fine internal structures, is evident. • Key words: Trilobita, Dalmanitidae, exoskeleton microstructure.

BUDIL, P. & HÖRBINGER, F. 2007. Exoskeletal structures and ultrastructures in Lower Devonian dalmanitid trilobites of the Prague Basin (Czech Republic). Bulletin of Geosciences 82(1), 27–36 (4 figures, 1 table). Czech Geological Survey, Prague. ISSN 1214-1119. Manuscript received January 17, 2007; accepted in revised form March 7, 2007; issued March 30, 2007. • DOI 10.3140/bull.geosci.2007.01.27

Petr Budil, Czech Geological Survey, Klárov 3, 118 21, Praha 1, Czech Republic; budil@cgu.cz • František Hörbinger, Ke Zdravotnímu støedisku 120, 155 00 Praha 5, Czech Republic; Frantisek.Horbinger@cuzk.cz

This study continues previous work on the fluid-mechanical/rheological origin of stromatactid cavity systems. In contrast to our previous work, this study focuses specifically on the role of liquids in settling slurries. Experiments with increasing amounts of surfactants (and other solutes) in water provided evidence that the formation of stromatactis- shaped cavities can be significantly reduced, increased or structurally modified in this manner. Two artificial ‘mud-based’, complex particulate materials were used, simulating the compositions of their natural counterparts: a ‘clastic mixture’ and a ‘sponge spicule mixture’. Three results are particularly significant: Firstly, the magnitude of volumes of stromatactis-like cavities initially falls and then increases, with the lowest values corresponding to the initial amounts of surfactants. Secondly, a nearly perfect match between the behaviours of the two different materials was found. And, thirdly, the largest and most typical cavity shapes were experimentally produced under conditions of moderately increased surfactant concentrations, whereas subsequent over-saturation lead to the formation of massive infills instead of well preserved voids. • Key words: surfactants, polydisperse particulate systems, multiphase systems, pattern formations, experimental sedimentation, voids in sediment, carbonate sediments, stromatactis.

HLADIL, J., KOPTÍKOVÁ, L., RÙŽIÈKA,M. & KULAVIAK, L. 2007. Experimental effects of surfactants on the production of stromatactis-shaped cavities in artificial carbonate sediments. Bulletin of Geosciences 82(1), 37–50 (6 figures). Czech Geological Survey, Prague. ISSN 1214-1119. Manuscript received July 29, 2006; accepted in revised form February 26, 2007; issued March 30, 2007. • DOI 10.3140/bull.geosci.2007.01.37

Jindøich Hladil, Academy of Sciences of the Czech Republic, Institute of Geology, Rozvojová 269, 165 00 Prague 6, Czech Republic; hladil@gli.cas.cz • Leona Koptíková, the same address as the first author and Charles University, Faculty of Science, Institute of Geology and Palaeontology, Albertov 6, 128 43 Prague 2, Czech Republic; koptikova@gli.cas.cz • Marek Rùžièka, Academy of Sciences of the Czech Republic, Institute of Chemical Process Fundamentals, Rozvojová 135, 165 00 Prague 6, Czech Republic; ruzicka@icpf.cas.cz • Lukáš Kulaviak, the same address as the previous author; kulaviak@icpf.cas.cz

The foliar morphospecies Linopteris obliqua (Bunbury) Zeiller, 1899 was originally based on isolated pinnules from Middle Pennsylvanian (upper Westphalian) strata in the Sydney Coalfield in Nova Scotia, Canada. However, new finds from the type area, including segments of a cauline axis and some fronds, attached juvenile croziers, an attached ovule, and associated pre-pollen organ, allow for a more complete understanding of the whole Linopteris obliqua plant. It was arborescent, 9 m to 10 m tall, with fronds ca 7 m long. Ovules of the Hexagonocarpus-type were attached directly to the petiole near the base of the frond, and pre-pollen was produced by Potoniea-type structures. The plant produced seeds and pollen at different times to avoid self-pollination. Ovule production was periodic and accompanied by mass pinnule abscission. The venation, especially the areolate-vein geometry, is relatively invariable within the plant species, and thus provides the typus (blueprint) for distinguishing other linopterid species, especially when combined with two-dimensional probability surfaces, and traditional pinnule morphology. However, the venation must be viewed on the abaxial surface of the pinnules if it is to be reliably interpreted. The mode of vein reticulation is shown to be quite distinct from the anastomosis-pattern seen in the other medullosalean taxa, and is another character that separates the Potonieaceae from the rest of the order. • Key words: Pennsylvanian potonieacean linopterid tree, monoescious, reconstruction.

ZODROW, E.L., TENCHOV, Y.G.&CLEAL, C.J. 2007. The arborescent Linopteris obliqua plant (Medullosales, Pennsylvanian). Bulletin of Geosciences 82(1), 51–84 (34 figures, 5 tables). Czech Geological Survey, Prague. ISSN 1214-1119. Manuscript received December 6, 2006; accepted in revised version March 5, 2007; issued March 30, 2007. • DOI 10.3140/bull.geosci.2007.01.51

Erwin L. Zodrow, 503 Coxheath Road, Sydney, Nova Scotia, Canada B1R 1S1; Erwin_Zodrov@cbu.ca • Yanaki G. Tenchov, Geological Institute, Bulgarian Academy of Sciences, G. Bonchev Street, Block 24, 1113 Sofia, Bulgaria • Christopher J. Cleal, Department of Biodiversity and Systematic Biology, National Museum Wales, Cathays Park, Cardiff CF10 3NP,UK