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Ivo Chlupáč – Vratislav Kordulewith the Ptychagnostus atavus and particularly with the P.punctuosus Zones (sensu Robison 1984), i.e. the higherpart of the major Paradoxides paradoxissimus trilobitebiozone of the Baltic scheme.The latest described arthropods come from the Ellipsocephalushoffi – Rejkocephalus Zone, especially fromthe locality at Rejkovice, where Helmetia? fastigata sp. n.,Tuzoia sp., Forfexicaris? sp. and some other problematicalremains were found in association with Ellipsocephalushoffi (Schlotheim), Rejkocephalus rotundatus (Barrande),frequent small hyolithids (often with opercula), brachiopodsLindinella kordulei Mergl et Šlehoferová, rareKonicekion tix Šnajdr, and few other fossils. Ichnofossils(Mikuláš 2000) belong to Skolithos, Planolites, Teichichnusand Daedalus. The E. hoffi – Rejkocephalus Zonemight correspond to the lower part of the Paradoxidesforchhammeri Zone of the Baltic zonal scheme (the correlation,however, is still problematic).Rare remains tentatively reported as Forfexicaris? sp. fromthe Skryje-Týřovice Cambrian in the NW flank of the Barrandian,belong to the Eccaparadoxides pusillus Zone of theSkryje Shale, corresponding roughly to the lower (but not thelowest!) part of the Jince Formation of the Jince area.To summarize, the representatives of Tuzoia and alliedtuzoid arthropods occupy together with thin-shelled remainsdesignated as Forfexicaris? sp. a rather long stratigraphicinterval within the Middle Cambrian, particularlyin its higher part correlatable with the Paradoxides paradoxissimusZone. Rare finds of Helmetiids and other exceptionalarthropods occurring in later strata with theindex trilobite Ellipsocephalus hoffi can be correlated withthe lower part of the Paradoxides forchhammeri Zone ofthe Baltic scheme.Palaeoecological notesAll the arthropods described here come from the MiddleCambrian siliciclastic rocks, namely from siltstonesand silty-clayey shales. They occur in sequences markedby alternating influx of silt-clay-sand (greywacke) materialin irregular intervals of mm to tens of cm thickness(lithologic characteristics of the Jince Formation: Kukal1971, Havlíček and Kukal in Chlupáč et al. 1998). Interbedsof dark grey or grey-green greywackes are locallyfrequent but they are persistent on individual outcrops. Describedremains of arthropods derive exclusively fromshale or siltstone beds, they were newer found ingreywacke layers. This suggests that the presence of sucharthropods corresponds to intervals of more stable conditionsreflected in the fine-grained sedimentation.Frequent remains of marine benthic animals, namelylarge polymerid trilobites and less common but typicalechinoderms (carpoids, eocrinoids, edrioasteroids) and hyolithids,accompany the described arthropods. Agnostidsare also present, though they are not dominant. Accordingto the scheme established for the Jince Middle Cambrianby Fatka (2000) our arthropods belong in the shallow-waterlife zone, dominated by polymerid trilobites.The ichnofossils marked by common epi- andintrastratal traces indicate the widely distributed shallowwaterenvironment of the Cruziana and/or Skolithos-Cruziana Ichnofacies (comp. Mikuláš 2000).The co-occurrence with complete exoskeletons of smalland large trilobites and non- or incompletely disarticulatedechinoderms and the preservation of even thin shields excludeany longer transport of the studied remains. In ourview, the tuzoiid, helmetiid and probably also proboscicaridarthropods could be regarded as nektobenthic animalswhose habit might be compared with some trilobites: theymight be scavengers or filter-feeders rather slowly movingabove the sea floor (cf. consideration of Helmetia by Briggsin Conway-Morris et al. 1982).A different habit can be presumed in Forfexicaris? sp.with very thin cuticle. It might represent a pelagic elementless dependent on bottom conditions and shallow-waterrealms (this can be supported by its occurrence in theSkryje Shale in association with more common agnostids).ConclusionRare remains of large non-trilobite arthropods in theMiddle Cambrian of Bohemia are confined to the laterphase of the marine transgression cycle.The described arthropods show clear resemblances toother, particularly North American, Middle Cambrian faunas(especially the Burgess Shale of British Columbia andcoeval strata of Utah). Their rare occurrence and incompletepreservation, however, prevent adequately based palaeogeographicaland biostratigraphical conclusions from beingdrawn. The relationships indicate open migration possibilitiesand faunal exchange over vast areas, probably even betweenLaurentia and the presumed shelves of Gondwana, towhich also the Barrandian area belonged.All described arthropods lived in marine environmentwith marked terrigenous influx. However, their remainsare contained in finer-grained siltstone and combined siltstone-claystonelayers pointing to temporary intervals ofrelative stable and quieter sedimentation. These conditionscould be generally more suitable for preservation of thincarapaces of described arthropods. The occurrence of Helmetia?,Tuzoia, and Forfexicaris? in siltstones of the Ellipsocephalushoffi Zone with less diversified benthos mayindicate a tolerance to conditions of decreased salinity.A nektobenthic habit and a rather shallow-water environmentare presumed for the discussed arthropods (exceptForfexicaris? sp. as a possible pelagic element).Biostratigraphic conclusions are premature, but theavailable finds come mostly from the upper part of theJince Formation, where some decrease of diversity in benthicfauna is already observed. The correlation with themiddle and upper parts of the Paradoxides paradoxissimusZone (most finds) and possibly with the lowest part of theParadoxides forchhammeri Zone (the youngest finds) ofthe Baltic biostratigraphic scheme is most probable.178