In the classic section across the Silurian—Devonian boundary at Dnistrove (Podolia, Ukraine) the brachiopod fauna has never been studied in detail. This paper presents results of research on brachiopods from this important locality and time interval. Bed-by-bed collecting has enabled the detailed distribution of brachiopod taxa through the boundary beds to be revealed. Generally, the reference section at Dnistrove yields rather scarce but often well preserved brachiopods. Dayla bohemica and Dnestrina gutta can be regarded as characteristic species for the uppermost Silurian. A relatively high-diversity but low-abundance brachiopod fauna occurs in the lowest 1.8 m of the earliest Devonian. Only three forms have been found to cross the Silurian—Devonian boundary: the strophomenide Plectodontu (Plectodontu) murlae puntherae subsp. nov., the atrypide Gruciunellu (Sublepida) paulula sp. nov., and the spiriferide Howellellu (Howellella) latisinuata. A relatively narrow brachiopod-rich interval at 5.5 m above the Silurian—Devonian boundary yields 16 brachiopod species which probably indicate a setting near the lower limit of the photic zone equivalent to the Benthic Assemblage 3–4 boundary. Two new species and one new subspecies are described: Skenidioides tatyunae, Plectodontu (Plectodonta) marlae puntherae, and Gruclanella (Sublepidu) paulula.
The Silurian—Devonian sequence in Podolia is regarded as one of the most important extensively exposed sections across this boundary interval, in both its palaeogeography and palaeontology. The succession is exposed at many localities along the valleys of the Dniester River and its tributaries and has been studied by many geologists and palaeontologists since the 19th Century (see overview by Nikiforova 1954). Of particular interest are the Upper Silurian and Lower Devonian strata, which record a complete upward transition from open-marine (fossiliferous Pridoli limestone) through marginal-marine to fluvial (upper Lochkovian—?lower Pragian redbeds) facies. Notwithstanding the long history of investigation of the Podolian sections, many aspects of this Silurian—Devonian reference sequence remain poorly known. In recent years several paleontological investigations have broaden and deepen our knowledge of the Silurian—Devonian faunas and floras of Podolia (e.g., Baliński 2010; Drygant and Szaniawski 2012; Filipiak et al. 2012; Krzemiński et al. 2010; Olempska et al. 2012; Olempska et al. 2012; Voichyshyn 2011; Voichyshyn and Szaniawski 2012).
Although a review of all papers on the Silurian—Devonian brachiopods of Podolia is beyond the scope of the present study, there is no doubt that the classic and pioneering monograph of Kozłowski (1929) is the most important. Unfortunately, the entire Kozlowski's (1929) collection, including the type specimens of new species, was destroyed in Warsaw during the Second World War. The review by Nikiforova et al. (1985) of the brachiopod fauna described by Kozłowski (1929), including establishment of neotypes of his new species, was an important contribution to modern knowledge of the Silurian—Devonian brachiopods of Podolia.
The main aim of the present paper is to study the detailed distribution of the brachiopod fauna through the Silurian—Devonian boundary beds at the key section at Dnistrove village (former Volkovtsy; 48°32″16.9″N, 26°14′21.4″E). All the material was collected bed-by-bed in this section, which is the only locality known at present where the boundary beds crop out (Figs. 1, 2). The exposure was densely covered and overgrown by vegetation but has been improved by excavation during the present investigation. Although the faunal occurrences were listed from the Silurian—Devonian key sections of Podolia by Nikiforova et al. (1972), the brachiopods from the S–D boundary interval at Dnistrove were not studied in detail.
The spelling of geographic names and names of stratigraphic units based on them in the Podolian sequence has changed through time according to adoption from Russian, Polish, or Ukrainian languages. Efforts to stabilize these names have failed, unfortunately. Recently, a new Ukrainian transliteration has been introduced and this nomenclature is used in the present paper (see Fig. 1).
Institutionul ubbreviutions.—ZPAL, Institute of Paleobiology, Polish Academy of Sciences, Warszawa, Poland.
Other abbreviations.—BA, Benthic Assemblage; S–D, Silurian—Devonian.
The Late Silurian to Early Devonian succession of Podolia forms a continuous phase of marine sedimentation terminating in the Middle Devonian by erosional hiatuses. During Pridoli times, differential subsidence and sedimentation rates resulted in 700–800 m thickness of rocks in the southwestern part of Podolia and 150–160 m thick deposits in its eastern regions. Early Devonian sedimentation was characterised by gradual regression with shrinking marine environments and increasing terrigenous input in western areas (Drygant 2003).
The Silurian sequence terminates with the Trubchyn (upper part of the former Rashkov Beds) and Dzvenyhorod (former Dzvinogorod) beds of the upper part of the Skala Horizon (Figs. 1, 2). They are mostly calcareous, with 19 m thick, dark-grey, fossiliferous, nodular limestone predominating in the topmost interval. The Silurian-Devonian boundary is placed 3.2 m above this interval, in the middle part of a sequence of interbedded greenish-grey argillaceous shale and marl beds containing dark-grey limestone nodules (Małkowski et al. 2009; Drygant and Szaniawski 2012) and representing the lowermost part of the Khudykivtsi Beds. The index graptolite species Monograptus uniformis angustidens Přribyl, 1940 was recovered in shale interbeds within the nodular limestone layers at the reference Dnistrove section (Nikiforova et al. 1972; Nikiforova 1977). It appears that the Silurian—Devonian boundary at Dnistrove can be correlated quite reliably with the boundary at the stratotype section at Klonk, Czech Republic (Chlupac and Hladil 2000).
The fossil-rich, open-marine Lochkovian suite is an uninterrupted continuation of the Silurian marine deposits. The suite starts with the 180 m thick Borshchiv Horizon, which includes the Khudykivtsi (former Tajna) and Mytkiv (former Mitkov) beds (Figs. 1, 2). At the Dnistrove section only the lower part of the Khudykivtsi Beds and the uppermost part of the Dzvenyhorod Beds are exposed (Figs. 2, 3). The former consists of platy limestone and variably interbedded darkgrey argillaceous shale, marl, and marly to micritic limestone whereas the Dzvenyhorod Beds consists of dark-grey, nodular limestone interbedded with greenish-grey argillaceous shale and marl (Małkowski et al. 2009; Racki et al. 2012).
Although generally the reference section at Dnistrove yields rather scarce and sometimes poorly preserved brachiopods, a limited brachiopod-rich interval in beds 47–48, (i.e., at 5.5 m above the S–D boundary) is distinguished by a diverse, abundant, and well preserved fauna (Fig. 3). Podolian geochemical data (Małkowski et al. 2009; Małkowski and Racki 2009; Racki et al. 2012; Fig. 3) show a major positive δ13C shift beginning in the late Pridoli that reached peak values as strong as +4‰ in the Khudykivtsi Beds (earliest Lochkovian). The secular pattern of δ18O values recorded in the Podolian sections probably documents climatic changes: Malkowski and Racki (2009) suggest considerable cooling in the latest Silurian, together with possible hypersalinity and strongly limited primary production. This may explain, to some extent, the low frequency of brachiopod specimens preserved in the lowest part of the section at Dnistrove. Interestingly, a low frequency but relatively diverse brachiopod fauna occurs in the lowest 1.8 m of the Early Devonian. This interval correspond to an initial phase of the positive C-isotopic excursion recorded in the section (Fig. 3).
Material and methods
I sampled the section at Dnistrove during the spring seasons of 2004, 2005, 2008, and 2009. Macrofossils (predominantly brachiopods) were collected bed-by-bed by splitting them out of the rock. In addition, samples of approximately 2 kg each were taken from fossiliferous beds and then dissolved in dilute acetic acid to obtain phosphatic shells of inarticulate brachiopods. These are represented almost exclusively by one species of Opsiconidion Ludvigsen, 1974.
The bed-by-bed collecting of specimens shows precisely the distribution of brachiopod taxa in the S–D boundary beds (Fig. 3). Although the sediments are similar throughout the greater part of the section (see above), the differing brachiopod faunas indicate that the environment must have varied slightly.
Distribution of brachiopods and palaeoenvironments across the Silurian—Devonian boundary
The brachiopod fauna described here was collected from the interval spanning from the topmost 1.6 m of the uppermost Silurian to about 12.3 m of the lowermost Devonian (Khudykivtsi Beds of the Borshchiv Horizon). The fauna consists of 22 species and genera including two new species and one new subspecies, i.e., Skenidioides tatyanae, Plectodonta (Plectodonta) muriue puntherue, and Gruciunellu (Sublepidu) paulula. Four other forms are reported for the first time from Podolia. These are Leptuenu (Leptuenu) aff. altera Rybnikova, 1966, Chlupacina sp., Oglu senilis Havlicek 1987, and Camarium sp.
The topmost part of the Silurian exposed in the studied section contains brachiopods that are poorly differentiated taxonomically but nevertheless very characteristic for the time interval. The oldest species found in the section is Dayia bohemica Bouček, 1941. It is confined to the thin bedded nodular limestone occurring at about 1.3–1.6 m below the S–D boundary. It is especially numerous in bed -24 (1.6 m below the boundary) where the species forms monospecific nest-like clusters. D. bohemicu is known from several sections of the Pridoli Formation in Bohemia and from the Pridoli of Estonia, Lithuania, and Latvia (Havlíček and Storch 1990; Rubel 1977). According to Havlíček and Štorch (1990: 42) D. bohemica is a characteristic species for the uppermost layers of the Pridoli Series and it does not cross the S–D boundary. It seems that the species occurs in the exactly the same stratigraphic position both in Bohemia and Podolia. In Bohemia the species occurs in brachiopod banks for which Havlíček and Štorch (1990) proposed the Dayia behemica Subcommunity. Earlier Boucot (1975) noted that Dayia forms a low-diversity, single brachiopod genus community in quiet-water settings within Benthic Assemblage (BA) 3.
About 0.3 m higher in the section at Dnistrove Dnestrina gutta Nikiforova and Modzalevskaya, 1968 is distinctive and is confined to a few cm thick shale. A very similar species described as Dnestrina cf. gutta has been recorded in the topmost layers of the Niushiping Formation (uppermost Pridoli) in the Renheqiao section in western Yunnan, China (Jahnke et al. 1989). It seems that Dnestrina might be widespread geographically but restricted stratigraphically. The Eifelian “Dnestrina n. sp. A” (see Langenstrassen 1972; Cocks 1978) from Sauerland (Germany) and Dnestrina? mawei (Davidson, 1881) from the Wenlock of Great Britain are insufficiently known forms. Thus, both the species from Dnistrove, D. bohemica and D. gutta, do not cross the Silurian—Devonian boundary in the section and can be regarded, at least locally, as guide species for the uppermost Silurian. Besides these two species the topmost Silurian faunule shows also the first appearances of very sporadic Plectodonta (Plectodonta) mariae pantherae subsp. nov., Grucianella (Sublepida) paulula sp. nov., and Howellella (Howellella) lutisinuata Kozłowski, 1929. It should be noted that all these forms are characterised by small shell size rarely exceeding 5 mm in length. This latest Silurian assemblage represents a stressed and impoverished, relatively deep-water environment characterised by interbedded greenish-grey argillaceous shale and marl. Although no evident change in environmental conditions has been noted in the lowermost Devonian, Dnestrinu gutta and Duyiu bohemica do not cross the S–D boundary. Boucot (1975) proposed a low-diversity high dominance, quiet-water Gruciunellu Community in the Silurian non-reef communities (BA 4–5, partially BA 3) of the Uralian-Cordilleran and North Atlantic Regions. In the Dnistrove section Racki et al. (2012) described a closely analogous low diversity, quiet water Dnestrinu gutta Community for the assemblages dominated by that brachiopod.
An interval about 1.8 m thick immediately succeeding the Silurian—Devonian boundary consists of graptolite shale at the bottom, shale, marl with limestone nodules, and limestone, yielding a brachiopod fauna that is more prolific and taxonomically diverse, although numerically low-abundance, and usually poorly preserved. These strata indicate a prolonged influence of the open marine facies in which small brachiopods still predominate. The fauna includes 13 species (Fig. 3) of which Gracianella (Sublepidu) paulula sp. nov. occurs in large numbers in the shell bed -4 (about 0.4 m above the boundary). Only 3 species of those characteristic for the lowermost Devonian cross the S–D boundary and have their first appearance just below it. These are the strophomenide Plectodontu (Plectodonta) muriue pantherae subsp. nov., the atrypide Gracianella (Sublepida) paulula sp. nov., and the spiriferide Howellellu (Howellella) latisinuata Kozłowski, 1929. P. (P.) mariae pantherae is numerous higher in the section in the fossiliferous marly limestone beds 47–48 (about 5.5 m above the S–D boundary) and is distinguished by the preservation of an unique shell colour pattern (Baliński 2010) which can also be easily recognised in specimens from shell bed -4 (0.4 m above the boundary), and thus appears to be an useful supplementary taxonomic feature even for specimens derived from different facies sediments.
The lowermost 1.8 m of the Devonian strata at Dnistrove contains a total of 13 species. Ten of them are more common in slightly higher intervals and can be regarded as characteristic for the lower Devonian: Skenidioides tatyanae sp. nov., Resserella elegantuloides, Talentella crassiformis, Cymostrophia (Protocymostrophia) costatula, Clorinda pseudolinguifera, Sphaerirhynchia gibbosa, Lanceomyonia borealiformis, Oglu senilis, Lissatrypa leprosa, and Pseudoprotathyris infantilis.
The brachiopod content of the Silurian—Devonian boundary beds at Dnistrove indicates a gradual shallowing-upward depositional environment. At about 3 m above the S–D boundary poorly fossiliferous, rhythmic marl and limestone beds start to prevail. In the exposed section the most fossiliferous beds 47–48 appears without easily recognisable environmental change, as indicated by the rocks. These beds yield brachiopod assemblage consisting of 16 species of which 10 possessed medium-to large-sized shells. The increased size of the elements of the assemblage indicates more favourable environmental conditions. The most numerous are Sepatrypa (Septutrypa) secreta (27% of the assemblage), Plectodonta (Plectodonta) mariae pantherae subsp. nov. (13%), Sphaerirhynchia gibbosa (12%), Clorinda pseudolinguifera (11%), and Talentella crassiformis (7%). The assemblage is represented by members of 9 orders and is characterised by a variety of morphologic types and ecological adaptations (e.g., small to large, concavo-convex, biconvex to globose, smooth, ribbed to frilled, with or without functional pedicle). The brachiopods are well preserved with chiefly articulated specimens. The disarticulation of the shells and rarity of dorsal valves of Clorinda pseudolinguifera indicates current sorting, although the sorting was limited. The preservational characteristics of C. pseudolinguifera may indicate a mechanically weaker hinge structure which was more prone to disarticulation—as in majority of the pentamerides—of the deltidiodont type. In contrast, many other articulate brachiopods co-occurring in the beds 47–48 possessed cyrtomatodont dentition, i.e., rhynchonellides, atrypides, athyridides, and spiriferides.
The occurrence of numerous specimens of the colour-patterned Plectodontu (Plectodonta) mariae puntherae subsp. nov. in the assemblage from bed 47–48 seems to have a potential value in characterising some environmental settings of the fauna. Baliński (2010) suggested that the assemblage with colour-banded shells inhabited shallow-water depths related to the photic zone of roughly tropical-subtropical or warm—temperate belt. The dominance of S. (S.) secreta in beds 47–48 suggests that this assemblage may be compared to the Silurian non-reef quiet-water Duburiu (= Septatrypa) Community of Boucot (1975). According to Racki et al. (2012) the brachiopod and associated fauna from beds 47–48 at Dnistrove probably indicates a setting near the lower limit of the photic zone correlated with equivalent to the BA 3–4 boundary.
The majority of species reported here are well known from other sections in Podolia and were described in details in the several papers (e.g., Kozłowski 1929; Nikiforova 1954; Modzalevskaya 1968; Nikiforova et al. 1985). In consequence, there is no necessity to repeat detailed descriptions of the species reported in the previous papers, so that only short comments and photographic documentation are provided. New species and inadequately known as well as those not described from the section before are described in details.
Phylum Brachiopoda Dumerill, 1806
Order Strophomenida Öpik, 1934
Superfamily Strophomenoidea King, 1846
Family Rafinesquinidae Schuchert, 1893
Subfamily Leptaeninae Hall and Clarke, 1894
Genus Leptaena Dalman, 1828
Subgenus Leptaena (Leptaena) Dalman, 1828
Type species: Leptaena rugosa Dalman, 1828; Dalmanitina beds, Ashgil, Ordovician; Fårdalaberg (Varvsberget), Västergötland, Sweden.
Leptaena (Leptaena) aff. altera Rybnikova, 1966
Fig. 4A–J, L.
Material.—27 shells, partly embedded in sediment, 5 ventral valves, 4 dorsal valves, and about 60 fragments; all from beds 47–48 of the studied section, i.e., at 5.5 m above the S–D boundary.
Description.—Shell rather small, attaining usually 12–14 mm in width, transversally subrectangular outline, with length approaching 51–62% of width; anterior margin weakly arched, lateral margins straight to weakly concave, cardinal extremities extend forming pointed alae.
Ventral valve with a very gently convex posteror region and concave the rest of the disk, sometimes with a very weak median longitudianl elevation; peripheral rim elevated, anterolaterally forming often swellings or bulges; trail geniculated medialy at 70–90° from commissural plane, attaining 51–91% of disk length, medially gently concave (emarginate); umbo small, with distinct supra-apical hollowed outgrowth (pedicle tube); interarea very low, ranging 0.4–0.8 mm in height, apsacline, medially triangular, laterally sublinear, delthyrim covered apically by short convex pseudodeltidium, rest of delthyrium filled up with massive chilidium (Fig. 4E–G).
Dorsal disk flattened, but with very shallow median sulcus and gently convex flanks; trail separated from disk with a shallow peripheral trough which anterolaterally forms two shallow hollows corresponding to the bulges on the ventral valve; trail frequently with very weak medial convexity; interarea very low, 0.2–0.3 mm in height, linear, anacline; notothyrium covered by a convex, medially deeply grooved chilidium.
Interior of the ventral valve with subcircular muscle field, bounded laterally by ridges and divided in its anterior half by a short median ridge (Fig. 4I, J); dental plates obsolescent by secondary shell material, developed as thickenned ridges (Fig. 4I, J); teeth small, wide, crenulated (Fig. 4J2); internal surface outside the muscle area covered by sparse pustulae arranged in radial rows.
Dorsal interior with sub-triangular cardinal process lobes divided by a deep slit and expanding in width anteriorly; sockets triangular, usually shallow, broad, bounded posteriorly by the edge of the interarea and medially by sharp and straight inner socket ridges (Fig. 4L); adductor scars deeply impressed posteriorly in the thickened shell wall, poorly delineated anteriorly, and medially separated by wide, thickened myophragm (Fig. 4L); internal surface of the disk with thick tubercles around muscle field and much finer anteriorly and laterally.
Ornament multicostellate, costellae faint, delicate, 3.5–4.5 per mm, those on lateral parts of the trail sometimes thiner, up to 7 per mm; rugae usually weak, sometimes imperceptible.
Remarks.—The species differs from the majority of other leptaenids in having small shell dimensions, a transverse, subrectangular outline, usually straight to gently concave (emarginate) anterior margin, inconspicuous to absent concentric rugae, rather weak radial costellae, and an elevated peripheral rim on the ventral valve frequently forming swellings at anterolateral corners. A well preserved, distinct, supra-apical hollowed outgrowth (pedicle tube) on the studied ventral valves (Fig. 4C2) is very similar to that described and illustrated by Kozlowski (1929: 92, fig. 26) in Glossoleptaena emarginata (Barande, 1879) from the middle part of the Borshchiv Horizon. The studied specimens differ from G. emarginata in not having a strongly emarginate anterior margin, which is one of the diagnostic features of the latter taxon.
Externally the specimens from Dnistrove are almost identical to Leptuenu (Leptuenu) altera Rybnikova, 1966 from the Pagëgiai Formation (Ludlow) of Ezere borehole and the Wenlock of Akniste borehole, Latvia (Rybnikova 1966). Musteikis and Cocks (2004: fig. 4H–O) re-illustrated two of the three type specimens of Rybnikova's paper and figured several other specimens from the Telychian—Ludfordian of Lithuania. Rubel (2011) described and illustrated several specimens of the species from the Wenlock of Estonia, and Telychian—Ludfordian of Lithuania. The authors have also shown the external variability of L. (L.) altera. Although the holotype of the species (Rybnikova 1966: pl. 1: 4; Musteikis and Cocks 2004: fig. 4H) is slightly larger and has a more semicircular shell outline than the specimens from Dnistrove, all other specimens of L. altera from the Baltic region illustrated by Musteikis and Cocks (2004) and Rubel (2011) show the same details of the external morphology and interior as the material here studied. The remarkable similarity between these forms is very suggestive despite evident difference in their stratigraphic ranges. This is the main reason that the present earliest Devonian material from Dnistrove is described as only related to the Llandovery—Ludlow L. altera.
The Podolian specimens show also some resemblance to Letugoniu jouchimiunu Havlíček, 1967 from the Liteň and Kopanina formations (Silurian) of Bohemia (Havlíček 1967: 105–106, pl. 19: 7–9, 12, 13, 17–20, fig. 41A; Havlíček and Storch 1990: 77, pls. 13: 3, 15: 6, 7). The differences between the two species seem to be minor and are expressed mainly in a more rectangular shell outline of the former. It is possible that both species are also closely related although the latter is again older stratigraphically.
Family Amphistrophiidae Harper, 1973
Subfamily Mesodouvillininae Harper and Boucot, 1978
Genus Mesodouvillina Williams, 1950
Type species: Stropheodonta (Brachyprion) subinterstrialis seretensis Kozlowski, 1929; Chortkiv Horizon (Early Devonian); Bogdanovka, Podolia (Ukraine).
Material.—One slightly incomplete ventral valve wit preserved exterior. Bed 102, 11m above the S–D boundary.
Remarks.—A single, strongly exfoliated ventral valve was recovered from the upper part of the studied section. Unfortunately, its internal structure and details of shell ornamentation cannot be assessed, making generic determination of the specimen somewhat tentative.
Family Douvillinidae Caster, 1939
Subfamily Protodouvillininae Harper and Boucot, 1978
Genus Cymostrophia Caster, 1939
Type species: Leptaenas stephani Barrande, 1879; Koněprusy Limestone, Pragian (Lower Devonian); Koněprusy, Bohemia.
Subgenus Cymostrophia (Protocymostrophia) Harper and Boucot, 1978
Type species: Strophomena ivanensis Barrande, 1879; Kotýs limestone (Lochkov, Lower Devonian); Svatý Jan pod Skalou, Bohemia.
Cymostrophia (Protocymostrophia) costatula (Barrande, 1847)
Fig. 4K, N–P.
1967 Mesodouvillina costatula (Barrande, 1848); Havlíček 1967: 170–171, pl. 34: 7, 9–12; fig. 69.
1968 Mesodouvillina costatula (Barrande); Modzalevskaya 1968: pl. 27: 2, 3.
1985 Mesodouvillina costatula (Barrande); Nikiforova et al. 1985: 22.
Material.—47 specimens, mostly fragmentary, embedded in rock. The species occurs scarcely at 1.5 m (bed 7) above the S–D boundary, but becomes much more common at 5.5 m (beds 47–48) above the S–D boundary.
Remarks.—Specimens from the studied interval at Dnistrove appear to be conspecific with Stropheodontu (Brachyprion) cf. costatula from the Khudykivtsi Beds of Myszkowce as illustrated by Kozlowski (1929: pl. 3: 33). More recently, Podolian collections from the same stratigraphic interval were attributed to Mesodouvillinu costutulu (Modzalevskaya 1968; Nikiforova et al. 1985). The latter authors discussed the relationship of the Podolian material with the type specimens of C. (P.) costatula from the lower Devonian of Bohemia, as well as with C. (P.) costatuloides (Johnson, Boucot, and Murphy, 1973) from the Pridoli of Nevada. According to Nikiforova et al. (1985), the specimens described by Nikiforova (1954) from the Malinovtsy and Skala horizons are probably more closely related to C. (P.) costatuloides, whereas specimens from the Khudykivtsi Beds are conspecific with C. (P.) costatula. This may also apply to two specimens reported (but not illustrated) by Kozłowski (1929) from the Dzwinogorod Beds of the Skala Horizon.
Stratigraphic und geographic range.—The species was originally described from the Kotys limestone (Lochkov, Lower Devonian) of Bohemia (Barrande 1847; Havlíček 1967). Recently Iordan (1999) found the species in the Silurian (Wenlock) of the Bătrânesti borehole, Romania. Similar form is listed as Mesodouvillinu aff. costatula by Berdan et al. (1969) from the upper Silurian of Nevada. In Podolia the species occurs in the Khudykivtsi Beds of the Borshchiv Horizon.
Superfamily Plectambonitoidea Jones, 1928
Family Sowerbyellidae Öpik, 1930
Subfamily Öpik, 1930
Genus Plectodonta Kozłowski, 1929
Type species: Plectodontu mariae Kozłowski, 1929; Mytkiv Beds, Borshchiv Horizon (Lower Devonian); Krivche, Podolia (Ukraine).
Plectodonta (Plectodonta) mariae pantherae subsp. nov.
Fig. 5A–J, M–P.
1978 Plectodonta aff. maria Kozłowski; Modzalevskaya 1968: pl. 27: 39.
2010 Plectodonta sp.; Baliński 2010: 696, figs. 1, 2, 3A.
Etymology: After the spotted colour pattern resembling that in the panther.
Holotype: Complete articulated shell ZPAL Bp. 56/99; illustrated in Fig. 5A.
Type locality: Trench east of Dnistrove village, Podolia, Ukraine. Coordinates 48°32′16.9″N, 26°14′21.4″E.
Type horizon: Beds 47–48, Khudykivtsi Beds of the Borshchiv Horizon (Early Devonian).
Diugnosis.—Shell small, attaining 5.6 mm in width, transversely subrectangular to semicircular, with slightly alate cardinal extremities; ventral sulcus and dorsal fold; inner pair of the dorsal side septa diverge at 31°, beginning at some distance from the socket plates; ornament parvicostellate, about 70 to 100 costellae in adult specimens and 3–9 fine costellae between each major costella.
Material.—Two isolated shells and 175 specimens (mostly ventral valves) embedded in sediment. The subspecies is quite common at 5.5 m above the S–D boundary (beds 47–48). Two specimens have been revealed also at 0.4 m above the boundary and 3 other at 1.15 m below the boundary.
Description.—Shell small up to about 4.6 mm in length and 5.6 mm in width, with a length to width ratio of 0.51–0.70, having concavoconvex, transversely subrectangular alate to semicircular outline; anterior commissure rectimarginate, anterior margin arched, lateral margins rounded, usually weakly concave near the hinge line forming short, pointed ears or, less frequently, cardinal extremities angular; hinge line straight and wide, usually equals the greatest width of the shell, finely denticulate.
Ventral valve gently convex in lateral profile with slightly swollen umbonal region; beak small, blunt; interarea low, up to ca. 0.4 mm in height, apsacline, almost flat to weakly concave, margins of delthyrium diverge at about 88°, apically closed by small convex pseudodeltidium; supraapical forament very small, bordered by slightly elevated ring; sulcus wide but poorly delimited laterally, with a median primary costa, on some specimens better marked at about midlength (about 0.5–2 mm from the beak, i.e., where lateral borders of the sulcus accomodate side septa of the dorsal valve), variable in profile from U-to V-shaped in cross-section, starting at umbo.
Dorsal valve weakly concave, with the greatest concavity in the posterior region near fairly prominent, elongate dorsal protegular node; fold well marked and wide occupying about
Dorsal interior visible on one juvenile specimen 1.8 mm long (Fig. 5M), with papillose surface; papillae coarse on the central region, fine peripherally; socket plates small, widely divergent; two prominent side septa diverge at 31°, beginning posteriorly at a distance of 0.4 mm from the socket plates; second pair of side septa very weak and shorter, almost imperceptible due to the immaturity of the specimen; cardinal process trifid in posterior view, occupying large portion of the delthyrium.
Ventral interior poorly preserved, but a short and thick median septum in the most posterior region of a valve is visible; surface finely papillose (Fig. 5E).
Shell ornament unequally parvicostellate; about 70 to 100 costellae in adult specimens at the anterior margin and 3–9 fine costellae between each major costella (usually 3–5); growth lines sometimes visible, rather weak (Fig. 5C, O).
Remarks.—The subspecies from Dnistrove is common in the lowermost Devonian, but a few specimens also occur in the uppermost Silurian, i.e., just immediately below the S–D boundary. It is most closely related to the nominative subspecies of the type species of the genus, i.e., Plectodontu (P.) muriue mariae which seems to be a direct descendant of the former. P. (P.) mariae mariae occurs abundantly in the succeeding Mytkiv Horizon of several localities in Podolia (Kozłowski 1929; Nikiforova et al. 1985). The new subspecies differs from the nominative subspecies by a smaller, less transversely extended shell, a better marked ventral sulcus and dorsal fold, greater number of radial costellae (70 to 100 in P. [P.] mariae pantherae, 45–50 in P. [P.] mariae mariae; Jahnke et al. 1989, however, give a total number of 95–100 costellae for the Kozłowski's  subspecies), wider interspaces between major costellae, and more numerous fine costellae between each major costella (3–9 in P. [P.] mariae pantherue, 2–4 in P. [P.] mariae mariae). Internally both subspecies seem also very similar. The internal features of a single available dorsal valve of P. mariae pantherae are less pronounced than those in large specimen of Kozłowski's nominate subspecies (see Kozłowski 1929: fig. 34A), but they appear virtually identical with those in juvenile specimen of P. (P.) mariae mariae representing the same individual stage of growth (see Kozłowski 1929: fig. 36C) as the former shown here on Fig. 5M.
The present subspecies differs from Plectodonta (P.) mimica (Barrande, 1879) from the Lochkovian of Bohemia (Havlíček 1967) in being somewhat smaller and by having a slightly more rectangular and alate shell outline and dorsal inner side septa appearing further anteriorly. According to Jahnke et al. (1989: 155) the Bohemian form should be regarded as a subspecies of P. (P.) mariae. The inadequatelly known Plectodonta moderatrix Havlíček and Storch, 1990 from the Kopanina Formation (Ludlow) of Bohemia (Havlicek and Storch 1990) is stratigraphically much older than P. muriue pantherae and differs in having less numerous costellae. Plectodontu petila Amsden, 1958 from the Haragan Formation (Lower Devonian) of Oklahma (USA; see Amsden 1958) is slightly larger than P. (P.) mariae pantherae and has rounded cardinal extremities. P. (P.) sanglangensis Xian, 1978 from the Tangxiang Formation of Guangxi, South China (Vogel et al. 1989) differs from the present subspecies in being smaller and having a longitudinal median furrow on the interior of the dorsal valve. P. (P.?) heterosinus Vogel, Xu, and Langenstrassen, 1989 and P. (P.) biplexa Xu, 1979, both from the same formation (see Vogel et al. 1989), are readily distinguished from the new subspecies by the ex-tremely transverse and alate outline and narrow, strong sul-cus and fold of the former, and by the elongate shell of the latter. P. (P.) orientalis Vogel, Xu, and Langenstrassen, 1989 also from the same formation and area, differs in having fascicostellate ornamentation.
Order Productida Sarycheva and Sokolskaya, 1959
Suborder Chonetidina Muir-Wood, 1955
Superfamily Chonetoidea Bronn, 1862
Family Strophochonetidae Muir-Wood, 1962
Subfamily Strophochonetinae Muir-Wood, 1962
Genus Chlupacina Havlíček and Racheboeuf, 1979
Type species: Chlupacina longispina Havlíček and Racheboeuf, 1979; Choteč Formation, Eifelian (Middle Devonian); Praha-Holyne, Bohe-mia.
Fig. 5K, L.
Material.—11 mostly incomplete specimens embedded in rock was found at 5.5 m above the S—D boundary (beds 47–48).
Remarks.—The collection is small and poorly preserved. The specimens show radial ornament which is weak to ab-sent posteriorly and better developed peripherally. The char-acteristic stronger median costa is usually well developed and reaches the anterior margin. On one specimen a 2.8 mm long (117% of the valve length), proximally cyrtomorph intraverse and distally gently arched spine is well preserved (Fig. 5L). Although preservation of spines on the studied specimens is rare, it seems that they are developed on the right side of the ventral valve only.
The present specimens differ from all chonetoid species known from the Siluro—Devonian of Podolia. The former re-sembles externally Pseudostrophochonetes mediocostalis (Kozłowski, 1929) from the lower Chortkiv Horizon (former Bogdanovka Beds) in having distinct median costa, but dif-fers mainly in thicker shell ribbing and a much older strati-graphic range. Small shell dimensions, presence of distinct median costa, and long spine developed on one side of the hinge line only suggest that the specimens from the studied section may be Chlupacina. Unfortunately, the paucity of the material and unknown internal shell structure does not allow for a more detailed determination.
Order Protorthida Schuchert and Cooper, 1931
Superfamily Skenidioidea Kozłowski, 1929
Family Skenidiidae Kozłowski, 1929
Genus Skenidioides Schuchert and Cooper, 1931
Type species: Skenidioides billingsi Schuchert and Cooper, 1931; Black River Formation, Sandbian, Ordovician; near the Ottawa River, Que-bec, Canada.
Skenidioides tatyanae sp. nov.
1929 Scenidium Lewisii (Davidson); Kozłowski 1929: 47–50, pl. 1: 20, 21; figs. 5–7, 37I.
1968 Skenidioides lewisi Davidson; Modzalevskaya 1968: pl. 27: 4–7.
1985 Skenidioides sp. nov.; Nikiforova et. al. 1985: 9.
Etymology: Species dedicated to Tatyana Lvovna Modzalevskaya in recognition of her work on Podolian brachiopods.
Holotype: Complete shell ZPAL Bp. 56/118; illustrated in Fig. 6A.
Type locality: Trench east of Dnistrove village, Podolia, Ukraine. Coor-dinates 48°32′16.9″N, 26°14′21.4″E.
Type horizon: Beds 47–48, Khudykivtsi Beds of the Borshchiv Horizon (Early Devonian).
Diagnosis.—Skenidioides with unisulcate anterior commis-sure, obtuse to gently rounded cardinal extremities, apsacline and usually concave ventral interarea, delthyrial angle attain-ing 31–38°, 26–31 costellae at the anterior margin; dorsal septalium deep, dorsal median septum reaching about 68% of the valve length.
Material.—Three complete shells, 57 ventral and 32 dorsal valves. Dimensions of the holotype (in mm): length 3.3, width 4.2, thickness 2.3, height of ventral interarea 1.2, width of hinge margin 3.7. The species is quite common at about 5.5 m (beds 47–48) above the S—D boundary. A few specimens have been also found 1.5 m (bed 7), 1.3 m (bed 5), and 0.7 m (bed -1) above the boundary. The species was also found in the Khudykivtsi beds at the Khudykivtsi vil-lage.
Description.—Shell small, up to about 5 mm in length, ventribiconvex, transversely elliptical to subpentagonal in outline; anterior commissure gently unisulcate, anterior mar-gin arched to slightly emarginate, hinge margin straight and wide but narrower than maximum shell width, cardinal ex-tremities obtuse to gently rounded, lateral margins rounded. Ventral valve sub-pyramidal with rather blunt beak, interarea high, apsacline, concave to only slightly concave, delthyrium open, sides diverging at 31–38°. Dorsal valve transversely elliptical, weakly convex, with wide, shallow, and poorly bounded laterally median sulcus occupying about 1/3 of the valve width; dorsal interarea wide and low, flat, anacline to nearly catacline.
Shell covered by strong, rounded costellae increasing by rare bifurcations or intercalations; ventral valve frequently with wider median intercostal space in which very thin, deli-cate single or paired costellae are usually developed; 26–31 costellae at the anterior margin. Growth lamellae rare, poorly developed, but anteriorly more obvious and crowded. Mi-cro-ornamentation of very fine, dense concentric lines, about 60 per 1 mm.
Ventral interior with deep, concave spondylium suppor-ted apically by wide, septum-like median thickening (Fig. 6N); teeth plate-like, wide (Fig. 6G, I). Dorsal valve with deep septalium bisected by thin median septum and triangu-lar, elongated cardinal processes at apex; median septum high, reaching about 68% of the valve length (Fig. 6M, O). Remarks.—The specimens studied here are most probably conspecific with those described in great details and illus-trated by Kozłowski (1929: 47–50, figs. 5–7, 37I; pl. 1: 20, 21) from the middle part of the Borshchiv Horizon as Sceni-dium lewisi (Davidson, 1848). Boucot et al. (1966: 364) sug-gested that cardinalia of the specimens from Podolia are of Skenidioides rather than Skenidium. Modzalevskaya (1968: pl. 27: 4–7) illustrated one shell from the Tajna beds (= Khu-dykivtsi Beds) at Dnistrove as Skenidioides lewisi. Nikiforova et al. (1985) suggested that Kozłowski's (1929) mate-rial, as well as their own new collections from the upper Khudykivtsi and Mytkiv beds, represent a new species that differ from Wenlock-Ludlow S. lewisii in a number of fea-tures. Indeed, Skenidioides lewisii (Davidson, 1848) from the Wenlock Limestone and Wenlock Shale of Dudley and Walsall (England) re-described by Bassett (1972: 35–37, pls. 5: 10, 6: 1–12) differs from the especies here described in having more restricted dorsal sulcus, higher and less concave ventral interarea, narrower delthyrium, narrower dorsal septalium, proportionaly longer dorsal median septum, and usually thicker costellae.
From Skenidioides robertsensis Johnson, Boucot, and Murphy, 1973 described from the Early Devonian of central Nevada (Johnson et al. 1973: 15, 16; pl. 10: 1–13) the new species differs in having a less transverse shell, narrower hinge margin with less acute cardinal extremities, and more concave, apsacline ventral interarea. The latter is readily dis-tinguishable from Skenidioides operosa Johnson, Boucot, and Murphy, 1976 from the Ludlovian of central Nevada (Johnson et al. 1976: 23, 24, pl. 29: 1–15), the Wenlock of Arctic Canada (Zhang 1989), and the Mackenzie Mountains of northwestern Canada (Jin and Chatterton 1997) in having less transverse shell, less acute cardinal extremities, shorter dorsal median septum, and finer, more numerous costellae. Skenidioides polonicus (Gürich, 1896) from the Middle De-vonian of the Holy Cross Mountains, Poland, which was redescribed by Biernat (1959: 16-25, pl. 1: 1–9, figs. 6–8; text-plates 1-2) and Halamski (2009: 72-74, pls. 10: 1–38, 12: 30; fig. 10) differs from the species described here mainly by having much thicker shell costellation, longer dorsal me-dian septum, and more acute, frequently mucronate cardinal extremities. Skenidioides tatyanae sp. nov. shows great ex-ternal similarity to Skenidioides henryhousensis Amsden, 1958 from the Henryhouse Formation (late Silurian) of Okla-homa, USA (see Amsden 1958), but differs from the latter by shorter and more rounded cardinal extremities, more con-cave ventral interarea, and narrower and stronger dorsal sulcus.
As suggested Nikiforova et al. (1985) the Silurian species described by Kozłowski (1929) from the Skala Horizon as Scenidium orthisiforme Kozłowski, 1929 probably belongs to Skenidioides. This form is poorly known and thus a nomen dubium (Nikiforova et al. 1985). It differs from the species here described by a more convex dorsal valve, the absence of the dorsal median sulcus, more rounded lateral margins, lower ventral interarea, and finer costation.
Strutigraphic und geographic range.—Kozłowski (1929: 50) found this species in several other localities from Podolia representing “l'étage de Borszczów”. Nikiforova et al. (1985: 9) collected new specimens representing this species from the Khudykivtsi and Mytkiv beds.
Order Orthida Schuchert and Cooper, 1932
Suborder Dalmanellidina Moore, 1952
Superfamily Dalmanelloidea Schuchert, 1913
Family Dalmanellidae Schuchert, 1913
Subfamily Resserellinae Walmsley and Boucot, 1971
Genus Resserella Bancroft, 1928
Type species: Orthis cunalis Sowerby, 1839; Coalbrookdale Formation, Wenlock, Silurian; Herefordshire, England.
Resserella elegantuloides (Kozłowski, 1929)
1929 Dalmanella elegantuloides sp. n.; Kozłowski 1929: 63–67, pl. 2: 1–16; figs. 9A, 10, 11.
Material.—Three complete shells, 19 ventral and 7 dorsal valves. The species was found 5.5 m above the S–D bound-ary (beds 47–48); single specimens were also recovered 0.4 and 0.95 m above the boundary (beds -4 and 1.5).
Remarks.—The species was described in great detail, both ex-ternally and internally, by Kozłowski (1929). Nikiforova et al. (1985) selected a neotype from the Mytkiv Beds of Verkh-nyakovtsy. The present specimens from Dnistrove fully agree externally with Resserella elegantuloides described by those authors.
Stratigraphic and geographic range.—The species is reported from the Khudykivtsi andMytkiv beds of the Borshchiv Hori-zon. It was also found in the lower Devonian of Nevada, USA (Johnson 1973: 1019, pl. 1: 16–20; Johnson et al. 1973: 17-18, pl. 14: 121) and New South Wales, Australia (Savage 1974: 16, 17; pl. 1: 25-29; Brock 2003: 118–119; pls. 7: 13–14, 8: 4–5).
Family Rhipidomellidae Schuchert, 1913
Subfamily Rhipidomellinae Schuchert, 1913
Genus Dalejina Havlíček, 1953
Type species: Dalejina hanusi Havlíček, 1953; Dvorce Limestone, Pragian; Prague Basin, Bohemia.
Dalejina frequens (Kozłowski, 1929)
1929 Rhipidomella frequens sp. n.; Kozłowski 1929: 83–86, pl. 3: 4–22; figs. 21B, 22, 23.
Material.—Four shells (2 of them slightly damaged), 4 dor-sal and 4 ventral valves. The present material was recovered from the Khudykivtsi Beds at Dnistrove at 5.5 m (beds 47–48) above the S—D boundary.
Remarks.—The studied specimens from Dnistrove, although rather scarce, are externally indistinguishable from specimens illustrated by Kozłowski (1929), Nikiforova (1954), and Niki-forova et al. (1985). The only difference is generally smaller shell size (not exceeding 8mmin length) attained by the speci-mens reported here. In this respect they are similar to Dalejina staszici Koz³owski, 1929, but the latter has a thicker shell with a more pentagonal outline resulting from narrower hinge mar-gin. D. staszici is a rare and stratigraphically older species, oc-curring only in the Skala Horizon.
According to Nikiforova et al. (1985) D. frequens is abundant in and restricted to the Mytkiv Beds (upper part of the Borshchiv Horizon). The present material, although not numerous, indicates that the species also occurs in the Khu-dykivtsi Beds.
Stratigraphic and geographic range.—Kozłowski (1929) found the species to range through the Borshchiv Horizon of Podolia. Nikiforova et al. (1985) reported it only from the Mytkiv Beds. Similar form described as D. aff. frequens was reported by Savage (1974: 19–20; pl. 3: 18–32; fig. 8A, B) from the lower Devonian of New South Wales (Australia).
Superfamily Enteletoidea Waagen, 1884
Family Draboviidae Havlíček , 1950
Subfamily Draboviinae Havlíček , 1950
Genus Talentella Johnson, 1990
Type species: Salopina submurifer Johnson, Boucot, and Murphy, 1973; Lochkovian, Lower Devonian; Nevada, USA.
Talentella crassiformis (Kozłowski, 1929)
1929 Dalmanella crassiformis sp. n.; Kozłowski 1929: 67–69, pl. 1: 30, 31; figs. 12A, 13.
1969 Salopina crassiformis (Kozłowski); Walmsley et al. 1969: 507–09.
Material.—7 shells, 53 ventral and 42 dorsal valves. The species occurs scarcely at 0.7 m (bed -1) above the S—D boundary but becomes much more common at 5.5 m (beds 47–48) above the boundary.
Remarks.—Describing the external variability of the species, Koz³owski (1929: 68) reported only 8 shells from 5 locali-ties. During the present investigation 7 additional shells have been recovered from the trench at Dnistrove. Nikiforova et al. (1985) selected a neotype from the Khudykivtsi Beds at Tselyuev-Myshakovtsy. Thus, this is a rather rare, small-sized (rarely exceeds 7 mm in length) species in Podolia.
The present specimens fully agree externally with those described by Koz³owski (1929) from the Borshchiv Horizon as Dalmanella crassiformis. More recently Nikiforova et al. (1985) assigned the species to Salopina Boucot, 1960, but eventually it was attributed by Johnson (1990) to his new genus Talentella Johnson, 1990. According to Kozłowski (1929) the species also occurs in the Malinovtsy and Skala horizons (Silurian) but Nikiforova et al. (1985) noted that it can be identified with certainty only from the Khudykivtsi Beds of the Borshchiv Horizon.
Stratigraphic and geographic range.—The species has been found in several localities in Podolia, all representing Khu-dykivtsi Beds of the Borshchiv Horizon. Walmsley et al. (1969: 509) reported the species from the lower Devonian of Nevada and northern Yukon Territory.
Order Pentamerida Schuchert and Cooper, 1931
Suborder Pentameridina Schuchert and Cooper, 1931
Superfamily Clorindoidea Rzhonsnitskaya, 1956
Family Clorindidae Rzhonsnitskaya, 1956
Subfamily Clorindinae Rzhonsnitskayia, 1956
Genus Clorinda Barrande, 1879
Type species: Clorinda armata Barrande, 1879; Zlichov Limestone, Emsian (Lower Devonian); Hlubočepy, Bohemia.
Clorinda pseudolinguifera Kozłowski, 1929
Figs. 8, 9.
1929 Barrandella (Clorinda) pseudolinguifera sp. n.; Koz³owski 1929: 137, pl. 6: 4–13; fig. 37: IV, fig. 40.
Material.—Six complete shells and more than 150 fragmen-tary valves and shells. Dimensions of the complete shells are given in Fig. 9. In the studied section the oldest (although fragmentary) specimens were recovered at about 1.0–1.7 m above the S–D boundary (beds 2, 5, 7, and 9). It becomes quite common at 5.5 m above the boundary (beds 47–48).
Remarks.—Contrary to the majority of species of the studied material from Dnistrove, Clorinda pseudolinguifera is mostly characterised by disjoined valves. This taphonomic character-istic can be explained by different mechanical resistance be-tween cyrtomatodont and deltidiodont hinge teeth. The latter, characteristic for majority of Pentamerida (including Clo-rinda), are much more susceptible to mechanical damage and disarticulation.
This species from the Borshchiv Horizon was described in great detail by Koz³owski (1929), including its internal shell structure and the variability of the external morphology, and Podolianmaterial have been considered by Nikiforova (1954), Modzalevskaya (1968), Gauri and Boucot (1968), and Nikifo-rova et al. (1985).Nikiforova et al. (1985) selected the neotype from the Mitkov beds cropping out at the mouth of Tsyganka stream. The new material contains adult as well as young shells, which illustrate some growth changes in the external morphology of the species (Figs. 8A–C, 9).
Stratigraphic and geographic range.—According to Nikiforova et al. (1985: 33), C. pseudolinguifera occurs through the Khudykivtsy Horizon, becoming common in the lower Mitkov Horizon where it sometimes forms shell banks up to 30–40 mm thick. Conspecific material has been reported from the early Devonian of the Urals (Gauri and Boucot 1968) and Altai Mountains (Gratsianova 1967) as well as from the top of Silurian and the lowest Lochkov of Bohemia (Havlíček and Štorch 1990).
Order Rhynchonellida Kuhn, 1949
Superfamily Uncinuloidea Rzhonsnitskaya, 1956
Family Hebetoechiidae Havlíček , 1960
Subfamily Sphaerirhynchiinae Savage, 1996
Genus Sphaerirhynchia Cooper and Muir-Wood, 1951
Type species: Terebratula wilsoni Sowerby, 1816; Elton Formation, Ludlow, Silurian; Mordiford, Herefordshire, England.
Sphaerirhynchia gibbosa (Nikiforova, 1954)
Figs. 10, 11, 12A–E.
1929 Camarotoechia (Wilsonia) Wilsoni (Sowerby); Kozłowski 1929: 159, pl. 7: 27–33 (not 34 = Sphaerirhynchia wilsoni?); fig. 50.
1954 Wilsonella wilsoni (Sowerby) var. gibbosa var. nov.; Nikiforova 1954: 110; pl. 11:5.
1968 Sphaerirhynchia gibbosa (Nikiforova); Modzalevskaya 1968: pl. 27: 40–43.
1978 Sphaerirhynchia gibbosa (Nikiforova); Rubel and Teller 1978: 477; pl 2: 16–18.
Material.—86 complete and 109 fragmentary or deformed shells. Statistical analysis of the main shell dimensions is given in Fig. 10. Sphaerirhynchia gibbosa is one of the most characteristic species in the studied section at Dnistrove. The first specimens appear in the interval at 1.3–1.5 m above the S–D boundary (beds 5 and 7). Slightly higher in the section (5.5 m above the boundary; beds 47–48) it becomes one of the most numerous taxa in the assemblage. Sporadically it occurs in beds 92, 96, 102, 105, 110, and 115.
Description.—Shell attaining about 18 mm in width, strongly dorsibiconvex in profile, subelliptical to subpentagonal in outline, globose, slightly wider than long; commissure serrate, moderately to strongly uniplicate. Ventral valve regularly convex in both lateral and anterior profiles; umbo massive but low, beak incurved; sulcus poorly defined, shallow, developed in anterior half, anteriorly forms subtrapezoidal to subrectangular tongue. Dorsal valve regularly and strongly convex with greatest convexity at about midvalve or slightly posteriorly; fold very low, poorly defined in anterior half of the valve.
Ribs fine, simple, extending from beaks, those at the anterior margin medianly grooved; 6–8 ribs on fold, 5–7 in sulcus, one pair of parietal ribs frequently present.
Interior of ventral valve with short, thin subparallel dental plates. In dorsal valve thin median septum attains less than half of the valve length and supports V-shaped septalium.
Dental plates slightly laterally convex, thin and short; outer hinge plates flat and horizontal; V-shaped septalium and median septum short; crura fairly long, slightly divergent, curving ventrally, with anterior surface concave distally (Fig. 11A, C).
Remarks.—Kozłowski (1929) described Camarotoechia (Wilsonia) wilsoni (Sowerby, 1816) (= Sphaerirhynchia wilsoni) from the Skala and Borshchiv horizons. Later, Nikiforova (1954) also collected the species from the older Malinovtsy Horizon. She found morphological differences between specimens from the Malinovtsy and Borshchiv horizons, and named the younger form as a new variety gibbosa. Nikiforova et al. (1985) then confirmed that specimens of Sphaerirhynchia gibbosa from the Khudykivtsi Beds of the Borshchiv Horizon are separable from true S. wilsoni as recovered by Nikforova (1954) from the Malinovtsy horizon.
Stratigraphic and geographic range.—According to Nikiforova et al. (1985), this is a common species in the Khudykivtsi Beds. S. gibbosa was also reported by Johnson et al. (1973) from the lower Devonian of Nevada.
Subfamily Hebetoechiinae Havlíček, 1960
Genus Lanceomyonia Havlíček, 1960
Type species: Terebratula tarda Barrande, 1847; Pridoli, Silurian; Dvorce, central Bohemia.
Lanceomyonia borealiformis (Siemiradzki, 1906)
1906 Rhynchonella borealiformis Szajnocha; Siemiradzki 1906: 171, pl. 7: 3–5.
Material.—9 complete shells and 7 fragments of shells and single valves. In the studied section the stratigraphically oldest specimens come from 1.0 m and 1.5 m above the S–D boundary (bed 2 and 5, respectively). Other specimens were recovered 5.5 m (beds 47–48) above the boundary and from a loose block representing the uppermost part of the section.
Description.—Shell up to 16.4 mm in length, dorsibiconvex, transversely subelliptical to subcircular in outline, slightly wider than long, uniplicate. Ventral valve regularly convex in lateral profile with strongly incurved beak in large shells; sulcus appears at about 7–8 mm from the umbo, rather shallow but clearly separated from flanks by slightly stronger ribs; tongue long, with convex bottom. Dorsal valve strongly convex; fold appears 5–6 mm from umbo, rather low, but clearly delimited laterally by slightly stronger bordering ribs. Posterior 5–9 mm of the shell surface smooth, anteriorly radially ribbed; ribs simple, rounded, very variable in number; 4–5 ribs on fold, 3–4 in sulcus, and 7–11 ribs on each flank.
Remarks.—This species was reported by Kozłowski (1929), as Camarotoechia (Wilsonia) tarda (Barrande, 1847), from the Borshchiv and Chortkiv horizons. Nikiforova et al. (1985) identified the species with certainty, however, only from the Khudykivtsi and Mytkiv beds of the Borshchiv Horizon. The specimens studied here from the Dnistrove section agree closely with those illustrated by Kozłowski (1929: pl. 7: 26) from the Borshchiv Horizon. He described the species in great detail, both externally and internally, and gave the statistic range of its morphologic variability.
Stratigraphic and geographic range.—Nikiforova (1954) reported the species from several localities in Podolia from the Borshchiv Horizon. Although Kozłowski (1929) and Nikiforova (1954) reported the species from many localities in Podolia they did not list Dnistrove among them. Later, however, Nikiforova et al. (1972) mentioned L. borealiformis from Volkovtsy (= Dnistrove).
Order Atrypida Rzhonsnitskaya, 1960
Suborder Atrypidina Moore, 1952
Superfamily Atrypoidea Gill, 1871
Family Atrypidae Gill, 1871
Subfamily Spinatrypinae Copper, 1978
Genus Oglu Havlíček, 1987
Type species: Terebratula semiorbis Barranae, 1847; Koněprusy Limestone, Pragian (Lower Devonian); Koněprusy, Bohemia.
Oglu senilis Havlíček, 1987
Figs. 13, 14H–J, M.
1987 Oglu senilis sp. n.; Havlíček 1987: 83–84, pls. 2: 7, 4: 1.
Material.—51 complete and 37 damaged shells. The species is quite common in beds 47–48 (5.5 m above the S–D boundary); a single specimen was also collected at 1 m above the boundary (bed 2), and another was found in a loose block from the uppermost part of the section (lower part of the Khudykivtsi Beds).
Description.—Shell rather small, usually up to 15 mm in length, slightly elongate to transverse, circular to shield-shape in outline, dorsibiconvex; hinge line short, nearly straight to slightly angular; maximum width posterior to midlength; anterior commissure rectimarginate to very weakly and broadly arched distally.
Ventral valve convex posteriorly, laterally and anteriorly planar to weakly concave; beak minute, incurved, interarea poorly defined, low, anacline; sulcus absent or very weak, almost imperceptible. Dorsal valve convex to strongly convex, greatest convexity slightly posterior to midvalve, fold not developed.
Ribs relatively coarse, undulose, especially posteriorly; 8 and 7 ribs near hinge margin on ventral and dorsal valves, respectively; ribs increasing usually by intercalation on dorsal and bifurcation on ventral valve; at anterior margin the total number of ribs ranges 17–20, exceptionally up to 25; ventral midrib pair slightly raised; growth lamellae undulating, extending into short trails and spines, the latter developed on both valves reaching up to 3.5 mm in length.
Interior of ventral valve with recognisable dental nuclei, thick pedicle callist developed into a collar in one of the sectioned shells (Fig. 13B); teeth stubby, subdorsally directed, with well-developed lateral lobes. Dorsal valve with distinct subtriangular in section median ridge; hinge plate umbonally lined with comb-like layer.
Remarks.—This rather small-sized atrypid is characterised by its shield shaped, dorsibiconvex shell ornamented by thick ribs, weakly undulating growth lamellae, and numerous short to quite long spines on both valves (Fig. 14M). The studied specimens externally resemble Spinatrypa Stainbrook, 1951, in shell shape, convexity, and spinose ornamentation, but they differ in their less undulose ribs, absence of dental plates, and by their occurrence much below the known stratigraphic range of the latter genus. Externally, the Podolian specimens also resemble Isospinatrypa Struve, 1966, in many respects, differing by having an evident dorsibiconvex shell instead of a biconvex to weakly dorsibiconvex profile as in the latter genus. They are also very similar externally and internally to inadequately known genus Oglu Havlíček, 1987 (see remarks in Copper 2002: 1412). It seems that Podolian species is conspecific with O. senilis Havlíček, 1987, which was described from a corresponding time interval (lowermost part of the Lochkov Formation) in central Bohemia (Havlíček 1987). The differences between them appear rather minor and are expressed in the presence of spinosity on both valves and slightly larger shell of the specimens from Dnistrove, which are up to 16 mm in width (in comparison to 12.5 mm in the Bohemian species; Havlíček 1987: 83). According to Havlíček (1987) the spinose ornament in Oglu occurs on dorsal valves only, but it seems probable that the absence of spines on the ventral valves may be related to the preservation. Because these differences seem rather minor, the specimens here described are regarded as conspecific with the Bohemian Oglu senilis Havlíček, 1987.
Stratigraphic and geographic range.—This species was not described from Podolia either by Kozłowski (1929) nor Nikiforova (1954). Originally the species was described by Havlíček (1987) from the lowermost part of the Lochkov Formation (Kotýs Limestone, Lochkov) in central Bohemia.
Family Atrypinidae McEwan, 1939
Subfamily Atrypininae McEwan, 1939
Genus Gracianella Johnson and Boucot, 1967
Type species: Gracianella lissumbra Johnson and Boucot, 1967; Robert Mountains Formation, Ludlow (Silurian); Robert Mountains, Nevada, USA.
Subgenus Gracianella (Sublepida) Mizens and Sapelnikov, 1982
Type species: Terebratula sublepida Verneuil, 1845; Pridoli, Upper Silurian; the Urals, Russia.
Gracianella (Sublepida) paulula sp. nov.
Etymology: From Latin paulula, in reference to the very small shell.
Holotype: Complete shell ZPAL Bp. 56/183; illustrated in Fig. 14F.
Type locality: Trench east of Dnistrove village, Podolia, Ukraine. Coordinates 48°32′16.9″N, 26°14′21.4″E.
Type horizon: Bed -4, lowest part of the Khudykivtsi Beds of the Borshchiv Horizon (Early Devonian).
Diagnosis.—Very small, lenticular, subcircular in outline with pointed ventral beak; distinct, apsacline to nearly orthocline ventral interarea, delthyrium open; ribs thick, about 8–10 on each flank, increasing by intercalation and bifurcation on both valves; ventral midrib pair prominent, divided by deep interspace with a thin, thread-like median costella; dorsal valve with well marked, wide sulcus and thick and simple median rib; lacking distinct concentric lamellose ornamentation.
Material.—109 complete shells and 53 fragmentary specimens. This species is quite common in the shale at 0.4 m (bed -4) above the S–D boundary. A few specimens were also found at 1.5 m (bed 7) above the boundary, as well as 0.2 m (bed -10) below it. In the studied section this short-ranging species occures about 1.1 m above the last occurrence of Dnestrina gutta and 1.2 m above Dayia bohemica (see Fig. 3).
Description.—Shell small, up to about 4 mm in length, biconvex, lenticular, subtriangular posteriorly and subcircular anterolaterally in outline, approximately as wide as long or slightly wider, widest slightly anteriorly to midlength; anterior margin rounded to weakly emarginate, hinge line short, almost straight, anterior commissure weakly sulcata.
Ventral valve weakly convex, slightly carinate, subtriangular in anterior profile; ventral beak pointed, interarea distinct, flat, apsacline to nearly orthocline, up to 0.6 mm in height; delthyrial cover not preserved. Dorsal valve weakly convex, subcircular to transversely elliptical, with weak to moderate median sulcus originating near umbo and widening markedly anteriorly.
Shell ornamented with thick radial ribs originating near umbos and delicate concentric, non-lamellose growth lines; ribs thickening anteriorly, separated by equal in width inter-spaces, increasing by intercalation and bifurcation on both valves; about 8–10 ribs on each flank; ventral midrib pair slightly carinate, thicker and more strongly elevated than lateral ribs, bifurcating laterally usually 3–4 times, separated by deeper and wider median interspace, the bottom of the interspace with a simple, very thin and low thread-like median costella; dorsal median rib simple, thicker than lateral ones, rarely with a very weak median furrow.
Remarks.—The main features of the specimens are very small and prominently ribbed shell, generally rounded outline with gently rounded to slightly emarginate anterior commissure, weakly carinate ventral midrib pair with deep median interspace occupied by thin median costella, sulcata dorsal valve with distinct simple median rib, apsacline to orthocline ventral interarea, and open delthyrium. Although the specimens are numerous they are frequently compressed by sediment compaction and sparitic filling of the interior, making study of the shell interior impossible. The small shell dimensions and character of the shell ribbing suggest assignment to Gracianella (Sublepida) Mizens and Sapelnikov, 1982.
While erecting Gracianella (Sublepida), Mizens and Sapelnikov (1982) included four species within the subgenus, Terebratula sublepida Verneuil, 1845 (type species), Gracianella plicumbra Johnson and Boucot, 1967, G. crista Johnson and Boucot, 1967, and G. cryptumbra Johnson, Boucot, and Murphy, 1973. The type species G. (Sublepida) sublepida was originally described by Verneuil (1845) from the uppermost Silurian of the east slope of the Urals, Russia (a probable topotype shell is shown here in Fig. 14K; see also Mizens and Sapelnikov 1982; Breivel and Breivel 1988). Conspecific specimens have been reported by Modzalevskaya (1968: pl. 15: 4–7) and Nikiforova et al. (1972: 89, 227) from the uppermost Silurian beds of the section at Dnistrove as Atrypa sublepida and Zygospiraella sublepida, respectively. It should be noted, however, that Grucianella (Sublepida) sublepida occurs at Dnistrove about 0.6–3.6 m below the S–D boundary (see Nikiforova 1977: fig. 3), whereas G. (S.) paulula sp. nov. was found in the interval spanning from 1.5 m above the boundary to 0.2 m below it. Due to the poorly exposed lowermost part of the section at Dnistrove, G. (S.) sublepida was not found during the present investigations; however, one shell of the species from the locality from the Tatyana Modzalevskaya's (1968) collection is here presented for comparison (Fig. 14L). Thus, the ranges of the two species mentioned do not overlap, but are separated by an interval about 0.4 m thick in which Dnestrina gutta is very characteristic (Fig. 3; see also Nikiforova 1977: fig. 3). G. (S.) paulula sp. nov. differs from G. (S.) sublepida mainly in having a smaller shell, different ribbing pattern (presence of distinct ventral midrib pair divided by deep interspace), open delthyrium, and the absence of conspicuous, undulating growth lamellae.1980). Recently the genus Arctispira was considered as a possible subjective synonym of Ogilviella Lenz, 1968 (Copper 2002: 1432).
The present species differs from Gracianella plicumbra Johnson and Boucot, 1967 from the Ludlow of the Robert Mountains (Nevada, USA: Johnson and Boucot 1967; Johnson et al. 1976) and Bohemia (Havlíček and Štorch 1990), and the Pridoli of Yukon Territory (Canada: Jackson et al. 1978; Lenz 1982) in having a wider shell, less rounded anterior commissure, wider dorsal sulcus with strong median rib, and a distinct midrib pair on the ventral valve. From Gracianella crista Johnson and Boucot, 1967, from the Ludlow of the Robert Mountains (Nevada, USA: Johnson and Boucot 1967; Johnson et al. 1976) and Bohemia (Havlíček and Štorch 1990), the new species is distinguished by a more circular instead of subrhomoidal shell outline, weaker ribs, a wider dorsal sulcus with strong median rib, and clearly divided median ventral ribs. Some finely ribbed specimens of a highly variable G. cryptumbra Johnson, Boucot, and Murphy, 1973 from the Pridoli of the Robert Mountains (Nevada, USA: Johnson et al. 1973) and Yukon Territory (Canada: Lenz 1977; Jackson et al. 1978) resembles G. (S.) paulula sp. nov, but the latter can be easily distinguished by its ribbing pattern. More often, however, the shells of the former species have fewer rather weak, and sometimes coalescent ribs, and a very broad, low median ventral rib.
Suborder Lissatrypidina Copper, 1996
Superfamily Lissatrypoidea Twenhofel, 1914
Family Lissatrypidae Twenhofel, 1914
Genus Lissatrypa Twenhofel, 1914
Type species: Lissatrypa atheroldea Twenhofel, 1914; Jupiter Formation, Llandovery, Silurian; Anticosti Island, Canada.
Lissatrypa leprosa Kozłowski, 1929
1929 Lissatrypa leprosa sp. n.; Kozłowski 1929: 167–169, pl. 5: 15–21; figs. 54, 55.
1968 Lissatrypa leprosa Kozl.; Modzalevskaya 1968: pl. 27: 44–47.
1984 Lissatrypa neglecta sp. n.; Havlíček 1984: 220, pl. 1:6, 7; pl. 2: 3–8.
1990 Lissatrypa leprosa Kozłowski, 1929; Havlíček and Štorch 1990: 193, pl. 65: 9.
Material.—One almost complete shell was found in a loose block of limestone near the bottom of the Khudykivtsi Beds together with Clorinda pseudolinguifera Kozłowski, 1929 and Sphaerirhynchia gibbosa (Nikiforova, 1954).
Remarks.—Although the single available specimens can not be studied internally, its exterior is indistinguishable from that of L. leprosa Kozłowski, 1929. Nikiforova et al. (1985) selected a neotype of the species from the Mytkiv (= Mitkov) Beds of the Borshchiv Horizon at Ustje and re-figured several well-preserved specimens externally and internally.
Copper (2004: 110–111) listed 41 species assigned tentatively to the genus Lissatrypa Twenhofel, 1914.
Stratigraphic and geographic range.—According to Nikiforova et al. (1985) the range of L. leprosa extends through the Khudykivtsi and lower Mytkiv beds. Havlíček and Štorch (1990) described the species in the top of the Pridoli Formation and the lowermost part of the Lochkov Formation in Bohemia. The species was also described by Jahnke et al. (1989) from the Lower Devonian of Yunnan Province, China.
Family Septatrypidae Kozłowski, 1929
Subfamily Septatrypinae Kozłowski, 1929
Genus Septatrypa Kozłowski, 1929
Subgenus Septatrypa (Septatrypa) Kozłowski, 1929
Type species: Septatrypa secreta Kozłowski, 1929; Khudykivtsi (former Tajna) Beds, Borshchiv Horizon, Lower Devonian; Olkhovtsy, Podolia, Ukraine.
Sepatrypa (Septatrypa) secreta Kozłowski, 1929
Figs. 15A, B, 16.
1929 Septatrypa secreta sp. n.; Kozłowski 1929: 177, pl. 9:18–24; fig. 58.
Material.—122 complete and well preserved shells and 140 fragmentary specimens. In the studied section it appears at 5.5 m above the S–D boundary (beds 47–48) where it is the most numerous species, comprising 27% of the brachiopod assemblage. In addition, five specimens were recovered from loose blocks from the uppermost part of the section.
Remarks.—This is one of the most common brachiopod species in the studied section at Dnistrove. The studied material is clearly conspecific with S. secreta as described and illustrated in great detail by Kozłowski (1929: 177–179, fig. 58, pl. 9: 18–24), Nikiforova (1954: 128–129, pl. 14: 8–9), Nikiforova et al. (1985: 44–45, fig. 6, pl. 11: 9–11), Biernat and Godefroid (1992: 44–48, pl. 1: 57–67, figs. 1, 2) and Copper (2004: 126–127, figs. 86, 87) from Podolia. Statistical characteristics of the studied material from Dnistrove are given on Fig. 16.
Stratigraphic and geographic range.—According to Nikiforova et al. (1985) the species is confined to the lower part of the Borshchiv Horizon (Khudykivtsi Beds; former Tajna Beds).
Order Athyridida Boucot, Johnson, and Staton, 1964
Suborder Athyrididina Boucot, Johnson, and Staton, 1964
Superfamily Athyridoidea Davidson, 1881
Family Athyrididae Davidson, 1881
Subfamily Didymothyridinae Modzalevskaya, 1979
Genus Pseudoprotathyris Modzalevskaya, 1979
Type species: Protathyris infantile Kozłowski, 1929; Dzwinogorod beds, Skala Horizon, Silurian; Zvenigorod, Podolia.
Pseudoprotathyris infantilis (Kozłowski, 1929)
Figs. 17, 19G, H.
1929 Protathyris infantile sp. n.; Kozłowski 1929: 230, pl. 11: 47.
1986 Pseudoprotathyris infantilis (Kozłowski); Grunt 1986: 51, pl. 3: 2.
Material.—11 more or less complete shells and 6 fragmentary specimens. The species were found at Dnistrove in interval at 0.3–1.2 m 1.3 m above the S–D boundary (beds -5, -4, -3,-1, 1.5, and 4).
Dimension of the two figured shells (in mm; see Fig. 19G, H, respectively): length, 5.3, 5.7; width, 4.5, 5.2; thickness, 2.5, 2.6.
Remarks.—The specimens from Dnistrove found at the base of the Khudykivtsi Beds appear to be conspecific with P. infantilis as described by Kozłowski (1929: 230–231, pl. 11: 47) from the Dzvenyhorod Beds of the Skala Horizon (former Dzwinogorod Beds) and by Modzalevskaya (1979: 60–62, pl. 4: 6–8, text-fig. 11) from the Dzvenyhorod, Khudykivtsi, and Mytkiv beds. Nikiforova et al. (1985) noted that the species is most common through the Khudykivtsi Beds. They selected a neotype of the species (Nikiforova et al. 1985: 54, pl. 14: 11) from the Dzvenyhorod Beds at the village of Dzvenyhorod. Two shells from Dnistrove are illustrated here (Fig. 19G, H) together with serial sections of one shell (Fig. 17).
Stratigraphic and geographic range.—As noted by Nikiforova et al. (1985) P. infantilis appears in the Dzvenyhorod Beds (uppermost Silurian) and ranges through the Khudykivtsi and Mytkiv beds (lower Devonian).
Superfamily Meristelloidea Waagen, 1883
Family Meristidae Hall and Clarke, 1895
Subfamily Meristinae Hall and Clarke, 1895
Genus Camarium Hall, 1859
Type species: Camarium typum Hall, 1859; Lower Helderberg Group, Lochkovian, Early Devonian; Cumberland, Maryland, USA.
Material.—Two slightly damaged and three complete juvenile articulated shells. The specimens were recovered at 5.5 m above the S–D boundary (beds 47–48).
Remarks.—The present specimens resemble some meristids in the general shell shape and in the presence of a shoe-lifter, which can be seen as a result of shell exfoliation in the umbonal region of one ventral valve. That is also supported by serial sections (Fig. 18), which confirm the presence of dental plates and a shoe-lifter in the ventral valve, together with a long and high dorsal median septum supporting a narrow, Y-shaped septalium. The absence of mystrochial plates in the sectioned specimen indicates that this form most probably represents Camarium. The specimens are ventribiconvex, subcircular in outline and possess a strongly incurved ventral beak, an extremely weak dorsal fold and ventral sulcus, which result in a weak uniplication of the anterior commissure in large and thick individuals. Kozłowski (1929) identified several meristid specimens from the Mytkiv Beds (former Mitkov Beds) and a few from the Khudykivtsi Beds (former Tajna Beds) as Merista passer (Barrande, 1848).
These differ from the specimens described here by their rather subpentagonal to subrhomboidal instead of circular shell outline, and their more weakly developed ventral sulcus. According to Nikiforova et al. (1985) M. passer is confined to the Mytkiv Beds, whereas rare specimens from the Khudykivtsi Beds appear to represent a new species. Unfortunately, the interiors of the sectioned specimens are incomplete or recrystallised, making impossible the investigations of brachiojugal structures and the material is too scarce to base a formal description of a new taxon.
Superfamily Dayioidea Waagen, 1883
Family Dayiidae Waagen, 1883
Dayia Davidson, 1881
Type species: Terebratula navicula Sowerby, 1839; Leintwardine Formation, Ludlow, Silurian; Herefordshire, England.
Dayia bohemica Bouček, 1941
Fig. 19 A–C.
1847 Terebratula navicula Murch.; Barrande 1847: 402, pl. 15: 4.
1879 Atrypa navicula Sow.; Barrande 1879: pls. 17-I: 1–7; 28-II: 1–16.
1929 Dayia navicula (Sowerby); Kozłowski 1929: 179–181, pl. 5: 22; fig. 59.
1941 Dayia navicula bohemica (nov.); Bouček 1941: 14, pl. 2: 1.
1982 Dayia bohemica Bouček, 1940; Modzalevskaya and Nikiforova 1982: 111, pl.1: 22.
1990 Dayia bohemica Bouček, 1941; Havlíček and Storch 1990: 206, pl. 68: 9–11.
Material.—34 complete or slightly damaged shells and about 130 fragmentary specimens. The species occurs in the lowermost exposed there layers, i.e., 1.3–1.6 metres below the S–D boundary (beds -21 to -24).
Remarks.—Dayia bohemica was initially proposed by Bouček (1941) as a new subspecies of D. navicula. Subsequently, however, it has been elevated to the species rank by Rubel (1977) and Havlíček and Štorch (1990).
According to Nikiforova et al. (1985), the specimens from the Dzwinogorod Beds near Dnistrove described by Kozłowski (1929) and Nikiforova (1954) as Dayia navicula (Sowerby, 1839) represent Dayia bohemica Bouček, 1941, which is known from approximately contemporaneous beds in the Pridoli of Bohemia. In addition to D. bohemica, Nikiforova et al. (1985: 45) also reported the occurence of typical D. navicula in slightly older horizons in Podolia, in the Grinchuk and Isakovtsy beds.
Stratigraphic and geographic range.—The species is known from several sections of the Pridoli Formation in Bohemia (Havlíček and Storch 1990). Rubel (1977) reported it from Pridoli of Estonia, Lithuania, and Latvia. In Podolia the species was reported from the Dzvenyhorod Beds of the Skala Horizon from the vicinity of Dzvenyhorod and Dnistrove villages.
Superfamily Anoplothecoidea Schuchert, 1894
Family Anoplothecidae Schuchert, 1894
Subfamily Anoplothecinae Schuchert, 1894
Genus Dnestrina Nikiforova and Modzalevskaya, 1968
Type species: Dnestrina gutta Nikiforova and Modzalevskaya, 1968; Pridoli, Upper Silurian; Moldavia, Podolia.
Dnestrina gutta Nikiforova and Modzalevskaya, 1968
Fig. 19D–F, J.
1968 Dnestrina gutta sp. nov.; Nikiforova and Modzalevskaya 1968: 207–210; pl. 1: 1–14.
1968 Dnestrina gutta Nikif. et T. Modz.; Modzalevskaya 1968: pl. 15: 15–19.
Material.—Two complete although compressed shells, and about 20 specimens embedded in sediment, mostly fragmentary. The present material was found 1.3–1.35 metres below the S–D boundary (beds -21 to -21.5).
Description.—Shell small, up to about 6.2 mm in length, subcircular to subovate in outline, slightly wider than long to subequal, widest slightly anteriorly to midlength, weakly concavo-convex; antero-lateral margins rounded, apical angle 110–120°, hinge line short, almost straight, anterior commissure gently arched ventrally.
Ventral valve weakly convex, with almost imperceptible median carina; interarea flat, apsacline to nearly orthocline, up to 0.5 mm in height. Dorsal valve weakly concave, subcircular to slightly transversely elliptical, with poorly marked narrow, angular median sulcus originating near umbo.
Interior of the ventral valve with distinct subtriangular, elongated, bulbous median thickening, rising gradually in height and lanceolate anteriorly; valve margin forming distinct, flat and wide peripheral rim; mantle canals poorly impressed, radiating. Dorsal interior not preserved, but probably with crenulated dental sockets (Fig. 19J).
Shell surface smooth, but with distinct lamellose growth lines, usually 12–14 on adult specimens.
Remarks.—This characteristic form was originally described by Nikiforova and Modzalevskaya (1968) from the Dzvenyhorod Beds of the Skala Horizon of Moldavia and Podolia. The latter is confined to the vicinity of the Dnistrove village where the present material comes from. In the studied section the species occurs approximately in the same layers as Dayia bohemica, i.e., in the lowermost beds exposed in the trench and representing the uppermost Silurian (Fig. 3).
Stratigraphic and geographic range.—The species is known from the the Dzvenyhorod Beds (uppermost Silurian) of Moldavia, Podolia, and Western Europe (Alvarez and Copper 2002). Similar form was described as D. cf. gutta by Jahnke et al. (1989) from the uppermost Silurian of Yunnan Province of China.
Order Spiriferida Waagen, 1883
Suborder Delthyridina Ivanova, 1972
Family Delthyrididae Phillips, 1841
Subfamily Howellellinae Johnson and Hou, 1994
Genus Howellella Kozłowski, 1946
Subgenus Howellella (Howellella) Kozłowski, 1946
Type species: Delthyris elegans Muir-Wood, 1923; Mulde Formation, Wenlock, Silurian; Gotland, Sweden.
Howellella (Howellella) latisinuata Kozłowski, 1929
1929 Spirifer (?Crispella) latisinuaus sp. n.; Kozłowski 1929: 197, pl. 11: 1–7.
1985 Howellella latisinuata (Kozłowski, 1929); Nikiforova et al. 1985: 48, pl. 13: 1–3.
Material.—Four complete shells and 37 fragments of shells and single valves embedded in rock. The specimens were recovered from several beds in the interval extending from 0.2 m below the S–D boundary (bed -10) up to 12.3 m above the boundary (bed 115).
Remarks.—Fragmentary material from Dnistrove conforms with this species, which was described from the basal part of the Borshchiv Horizon (Kozłowski 1929: 197–198, pl. 11: 1–7; Nikiforova et al. 1985: 48, pl. 13: 1–3), in having a small shell and very few, weak radial plications. The largest complete shell in the present material (see Fig. 20A) measures 8.2 mm in length and 10.7 mm in width. Nikiforova et al. (1985) designated the neotype of the species from the Khudykivtsi Beds exposed at Olkhovtsy village (about 8 km NW from Dnistrove).
Stratigraphic and geographic range.—Nikiforova et al. (1985: 48) confirmed that the species is confined to the Khudykivtsi Beds (former Tajna Beds).
Suborder Cyrtinidina Carter and Johnson, 1994
Family Cyrtinidae Fredericks, 1911
Genus Cyrtina Davidson, 1859
Type species: Calceola heteroclita Defrance, 1824; Middle Devonian, France.
Cyrtina praecedens Kozłowski, 1929
Fig. 20B, C.
1929 Cyrtina praecedens sp. n.; Kozłowski 1929: 207–211, pl. 11: 8–23; figs. 68, 70–75.
1985 Cyrtina praecedens Kozłowski, 1929; Nikiforova et al. 1985: 52–53, pl. 12: 3, 4 [full synonymy herein],
Material.—One complete but superficially corroded shell and one incomplete ventral valve, both from beds 47–48 (5.5 m above the S–D boundary) of the studied section at Dnistrove.
Remarks.–The species, as well as its variability, was described in great detail by Kozłowski (1929). More recently, Nikiforova et al. (1985) selected the neotype of the species from the Mytkiv Beds of Verkhnyakovtsy. The present material, although rather scanty, closely corresponds externally to Cyrtina praecedens. The studied specimens show clear punctation of the shell substance, pustulose microornamentaion, and presence of tichorhinum in the ventral valve.
Stratigraphic and geographic range.—According to Nikiforova et al. (1985), C. praecedens is one of the most common and characteristic species of the Borshchiv Horizon. It appears in the Khudykivtsi Beds but becomes especially common in the Mytkiv Beds. Savage (1969: 483–486, pl. 92: 1–44) described C. praecedens from the Lower Devonian (Siegenian) Mandagery Park Gormation of New South Wales and Drot (1964: 91) reported ?Cyrtina praecedens from the Gedinnian of Morocco.
Sincere thanks are extended to Mike Basset (National Museum of Wales, Cardiff, UK) for improvement of the English of an earlier version of the manuscript and Grzegorz Racki (Silesian University, Sosnowiec, Poland) for critical comments. To Tatyana L. Modzalevskaya (A.P. Karpinsky Russian Geological Research Institute, Sankt Petersburg, Russia) I owe my special thanks for the specimens of Gracianella (Sublepida) sublepida from Dnistrove and the Urals as well as for providing access to the collection from Podolia. The paper was greatly improved through reviews by Robin Cocks (Natural History Museum, London, UK) and Jisuo Jin (University of Western Ontario, London, Canada). This work has been supported by a grant on the geochemistry, stratigraphy, and palaeontology across the Silurian—Devonian transition in Podolia (No. N N307 057834) from the Ministry of Science and Higher Education to Hubert Szaniawski (ZPAL).