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Scanning electron microscopy of untreated and uncoated fracture sections of a secondary shell of a Cambrian (Furongian) linguloid brachiopod Ungula inornata (Mickwitz) in concurrent backscattered electron and secondary electron imaging regimes revealed phosphatized organic fibril-like nanostructures, less than 200 nm in diameter. By analogy with published data on a living lingulate genus Discinisca, the nanofibrils are interpreted as parts of the organic biopolymer matrix, which are composed of axial protein strands of bacula connected by chitin and participate in the formation of baculate sets. The nanofibrils are relevant structural units in the hierarchical structure of lingulate brachiopods with baculate shell structure. It is concluded that these structures are preserved by instant post-mortem precipitation of apatite. The shell structure of U. inornata is most similar to the other species of the genus Ungula Pander and the species of the genus Obolus Eichwald

Fossil skeletal apatites vary in their composition and can yield mixed biochemical, environmental and diagenetic information. Thus, it is important to evaluate the diagenesis spatially inside the skeleton. We study the cross sections of shells of the Furongian lingulate brachiopod Ungula ingrica from Estonia using the Attenuated Total Reflectance -Fourier Transform Infrared (ATR-FTIR) microspectroscopic and energy dispersive spectroscopic (EDS) mapping and show for the first time that different structural laminae of the shell have different chemical compositions. Compact laminae are rich in PO 4 3À , Na, Mg and poor in F and Ca. Porous (baculate) laminae are rich in carbonate anions, Ca and F, but contain less Na and Mg. The ATR-FTIR spectra show further differences in the m 2 carbonate region, where the IR band at 872 cm À1 in compact laminae is replaced by a strong band at 864 cm À1 in baculate laminae. The changes in shell apatite suggest different origins of the apatite phases. Compact laminae are likely chemically less altered and could potentially carry more reliable palaeoenvironmental or geochemical information than the apatite in baculate laminae, which is mostly authigenic in its origin. □ Apatite, attenuated total reflectance map-

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The type species of the brachiopod genus Bicarinatina Batrukova was first described by Kutorga in 1837 (Zweiter Beitrag zur Geognosie und Paläaontologie Dorpats und seiner nächsten Umbegebungen. St.-Petersbourg, 51 pp.) as Lingula bicarinata from the Middle Devonian sandstone beds now assigned to the Aruküla Regional Stage in Tartu, Estonia. Gravitis (1981, in Devon i karbon pribaltiki (Brangulis et al., eds), pp. 455-462. Zinatne, Riga) described eight new species of the genus Bicarinatina. Revision of the collections in St Petersburg and Riga showed that four of these species names should be considered as subjective junior synonyms of the type species Bicarinatina bicarinata (Kutorga) and that the type specimens of the remaining four new species were either juvenile or too poorly preserved for species-level identifications. Therefore, B. bicarinata should be considered the only valid species of the genus Bicarinatina occurring in the Middle Devonian on the Baltic plate, known from Estonia, Latvia, and northwestern Russia. The shell structure of B. bicarinata is baculate symmetrical, with the finest baculate sets in the innermost parts of the valves and thicker and aggregated baculi in outer parts, due to stronger taphonomic changes in outer parts of the shell. In cross section, the valves are 70-100 µm thick.