Indigenous demosponge spicules in a Late Devonian stromatoporoid basal skeleton from the Frasnian of Belgium

This paper records the first example of a demosponge spicule framework in a single specimen of a Devonian stromatoporoid from the Frasnian of southern Belgium. The small sample (2.5 × 2 cm) is a component in a brecciated carbonate from a carbonate mound in La Boverie Quarry 30 km east of Dinant. Because of the small size of the sample, generic identification is not confirmed, but the stromatoporoid basal skeleton is similar to the genus Stromatopora. The spicules are arranged in the calcified skeleton, but not in the gallery space, and are recrystallized as multi‐crystalline calcite. The spicules fall into two size ranges: 10–20 μm diameter and 500–2000 μm long for the large ones and between 5–15 μm diameter and 50–100 μm length for the small ones. In tangential section, the spicules are circular, they have a simple structure, and no axial canal has been preserved. The large spicules are always monaxons, straight or slightly curved styles or strongyles. The spicules most closely resemble halichondrid/axinellid demosponge spicules and are important rare evidence of the existence of spicules in Palaeozoic stromatoporoids, reinforcing the interpretation that stromatoporoids were sponges. The basal skeleton may have had an aragonitic spherulitic mineralogy. Furthermore, the spicules indicate that this stromatoporoid sample is a demosponge.     

Size and shape distribution of level-bottom tabulate corals and stromatoporoids (Silurian)

Baarli, B. G., Johnson, M. E. & Keilen, H. B. 1992 07 15: Size and shape distribution of level-bottom tabulate corals and stromatoporoids (Silurian).
Size and shape distribution of tabulate coral and stromatoporoid faunas were studied at two Lower Silurian sections in Norway on the Baltic platform and one section in eastern Iowa on the Laurentian platform. All the sections are dominated by storm beds with predominantly shallowing upward features; they differ from one another in clastic content and proximity to land. Most of the fauna lived below normal wave-base, but within the photic zone, on fine grained and firm bottoms. In all three localities, size clearly increases up-section for stromatoporoids, favositids, and heliolitids but it decreases for halysitids in the Oslo region. Sediment influx worked negatively on size but generally not so much as to affect average size. lurbulence in combination with decreasing sediment influx affected the size decrease in heliolitids up section. Nutrients and turbidity were of minor importance as growth controlling factors. Light intensity is the only factor that shows a pattern consistent with increased size up-section. Sediment influx alfected fauna composition and shape: heliolitids had the highest sediment tolerance and stromatoporoids had the lowest. Ragged skeletons were linked to tempestites. Corals and stromatoporoids reveal a population-specific response to environmental change, largely independent of benthic assemblage zones or communities. Tabulate corals, stromaroporaids, bathymetry, size variation. clastic input, benthic assemblages .     

Stromatoporoid-coral intergrowths in a Silurian biostrome

Four stromatoporoid species from a stromatoporoid biostrome in the middle Ludlow Hemse Beds, Gotland, Sweden, show intergrowths with syringoporid tabulate and rugose corals, and indicate close relationships between particular coral and stromatoporoid species. The stromatoporoid Clathrodictyon convictum always contains ?Syringopora and this tabulate is rarely found in the other stromatoporoids. C. convictum is also closely associated with Tryplasma flexuosum (rugosa) while Petrozium pelagicum (rugosa) occurs only in the stromatoporoids Plectostroma intermedium and Parallelostroma typicum. The microstructure of ?Syringopora within the stromatoporoids is composed of an inner lamellar layer and an outer radial layer of calcite crystals. Diagenetic alteration has affected the microstructure which differs from recently described Devonian forms having only a radial layer. This shows variability in the structure of the tabulates within stromatoporoids. Information is sparse on the range of such variation and assessment of the relative importance of taxonomic, palaeoenvironmental and diagenetic effects is not possible in the present sample. No evidence is found to prove the precise nature of the relationships; they were not parasitic but may have been mutually symbiotic, or (most probably) commensal. The results suggest that the corals selected the most suitable stromatoporoid species for their requirements. Stromatoporoid morphology may have had an important influence on the association, where corals are more abundantly associated with those stromatoporoid species which adopted a high profile. Overall the associations appear to have allowed the corals to explore higher energy habitats otherwise unavailable to their delicate branching structure.     

Parameterization of stromatoporoid shape

Kershaw, Stephen & Riding, Robert 1978 07 15: Parameterization of stromatoporoid shape. Lethaia , Vol. 11. pp. 233–242. Oslo. ISSN 0024–1164.
Stromatoporoid cross-sectional shape can be considered as a product of the interaction of three morphological variables: the relative proportions of basal, vertical and diagonal dimensions. The gross arrangement of internal lamination can be superimposed upon the resulting outlines. These shapes are taken to represent cross sections in any vertical plane through the centre of the coenosteum. This simple parameterization scheme is presented in triangular arrays which include the stromatoporoid morphotypes laminar, domical and bulbous, and varieties of them together with forms not utilized by stromatoporoids. Dendroid and irregular forms are too complex to be readily included in the scheme. Smooth and ragged varieties of laminar and domical forms are distinguished and related to sedimentation on the flanks of the coenosteum. Two types of mutual arrangement of latilaminae within the coenosteum are recognized: enveloping, where they completely overlap previous latilaminae, and non-enveloping, where they do not. Laminar-domical-bulbous forms represent a series generated mainly by reduction of the basal dimension. They commonly exhibit enveloping latilaminae except in ragged varieties and some extended domes. Measurement of defined dimensions in the field allows stromatoporoid morphotypes to be plotted onto the triangular arrays and provides a rapid method of displaying the range of forms present.     

Significance of stromatoporoids in Jurassic reefs and carbonate platforms—concepts and implications

Although many case studies describe stromatoporoid-rich Jurassic reefs, there are only few reliable data as to their distribution pattern. This is in part due to a largely taxonomic and systematic focus on the enigmatic stromatoporoids which now are interpreted as a polyphyletic informal group of demosponges by most specialists. The common co-occurrence of Jurassic scleractinian corals and stromatoporoids might, at first hand, point to very similar environmental demands of both organismic groups, but autecological considerations as well as evaluation of stromatoporoid distribution patterns should allow for a much more refined interpretation. This study concludes that Jurassic corals and stromatoporoids show a relatively broad overlap of environmental demands but their maximum ecological tolerances appear to differ considerably. Jurassic corals were dominating in mesotrophic to mildly oligotrophic, slightly deeper settings, where they largely outcompeted stromatoporoids. On the other hand, stromatoporoid growth was particularly favoured in very shallow water, strongly abrasive, high-energy settings as well as in possibly overheated waters. Many taxa and growth forms were very tolerant towards frequent reworking and redistribution, a feature which is compatible with the sponge nature of the stromatoporoids. As such, stromatoporoid facies may be common in low-accommodation regimes, giving rise to frequent “shelf shaving” and redistribution across wide shelf areas. The mixed coral-stromatoporoid reefs from the margins of isolated Intra-Tethys platforms are interpreted to be indicative of oligotrophic normal marine waters. This is corroborated by statistical cluster analysis of stromatoporoid taxa from representative areas. In addition, Arabian stromatoporoid occurrences might have been adapted to overheated and slightly hypersaline waters. There also are a few exceptional stromatoporoid taxa which might have had environmental tolerances different from the bulk tolerances of other Jurassic stromatoporoids. Part of our interpretations are preliminary and should stimulate further research. However, the present results already help explain the observed compositional differences between Jurassic North Tethys/North Atlantic, Intra-Tethys, and South Tethys shallow-water reefs and platforms.     

Microevolutionary implications of clinal variation in the Paleozoic bryozoan Streblotrypa

Hageman, S.J. 1994 10 15: Microevolutionary implications of chal variation in the Paleozoic bryozoan Streblotrypa Lethaia Ideally, studies of microevolution, including those of patterns and rates of speciation, need to account for features of geographic and ecophenotypic morphologic variation. These factors can provide primary sources of variation for evolution to act upon. They can also, however, produce variation among characters that are not directly related to speciation events, thus confounding recognition of larger evolutionary patterns. Because of limitations of geologic settings, features of morphologic variation associated with geographic and ecophenotypic variation are difficult to constrain and are often neglected. Consequences of ignoring potential geographic variation in microevolutionary studies are varied. The likelihood of observing stasis or gradation may increase or decrease depending on initial assumptions. A series of tests that place reasonable limits on potential errors, however, can strengthen conclusions from empirical microevolutionary studies. Late Paleozoic cyclothems of the North American Midcontinent provide an excellent opportunity to study patterns of microevolution and concomitant ecophenotypic and geographic variation. Based on multivariate analysis of 28 morphometric characters, specimens of the rhabdomesine bryozoan genus Streblotrypa, collected from eight coeval localities distributed along a 300 km transect, exhibit a morphologic cline associated with thickening of the skeleton from south to north. Additional specimens were collected from five younger localities to test for temporal and ecologic variation. The range of observed morphologic variation from a single horizon was as great as that observed over the entire stratigraphic sequence from varied lithologies. This indicates a pattern of overall morphological stasis through the interval studied. Bryozoa, clines, microevolution, variability, geographic variation, Carboniferous.     

An association between the stromatoporoid Diplostroma yavorskyi Nestor and calcareous algae from the Much Wenlock Limestone, England

Intergrowths of the stromatoporoid Diplostroma yavorskyi Nestor with calcareous algae are described for the first time from the Much Wenlock Limestone of Wenlock Edge, England. The intergrowth developed as irregular. nodular growth-forms which initiated around a nucleus of biomicrite sediment or skeletal clasts. The paired stromatoporoid laminae characteristic of this species form regular alternations throughout substantial portions of the skeleton with the calcareous algae Girvanella sp., Rothpletzella sp., Wetheredella sp. and Rhabdoporella sp., and micrite. Nodular growths developed as a result of intermittent rolling on the sea floor. The nature of the periodic intergrowth of different taxa suggests that the stromatoporoid grew on firm substrates by lateral growth at an edge zone. Epiphytes encrusted areas of the stromatoporoid skeleton devoid of soft tissue. □ Stromatoporoid. calcareous algae. epiphyte. intergrowth. Wenlock.     

Vertical motion detectors and their synaptic relations in the third optic lobe of the fly

The synaptic relations of the giant vertical cells in the lobula plate of the fly were investigated using electron microscopical procedures and Lucifer yellow dye backfill and injection techniques. Histological features of the giant vertical cells are described. The giant vertical cells are exclusively postsynaptic in the lobula plate. They function to integrate input from dense arrays of chemical synapses and have a wide spatial input from the lobula plate. The giant vertical cells are postsynaptic to perpendicularly occurring cells. There are two classes of cells presynaptic to the vertical cells, one of which contains large dense-core vesicles. The giant vertical cells are not the only cells postsynaptic to these two classes of perpendicualr cells. A second group of smaller tangential cells, the twin vertical cells, were also found postsynaptic to many of the same cells that synapsed with the giant vertical cells. The twin vertical cells and the giant vertical cells are therefore integrating some of the same information in the lobula plate.     

红豆草中含晶细胞的形态学研究

红豆草（Ｏｎｏｂｒｙｃｈｉｃｖｉｃｉａｅｆｏｌｉａｓｃｏｐ．）植株的所有器官中都分布有含晶细胞,其结晶的类型主要为棱晶,此外还有砂晶。在营养器官中,含棱晶的细胞主要分布在维管组织之中或外围。横切面上,棱晶则几至几十块纵列成行存在,且常伴生于韧皮纤维旁,但每块棱晶各有一分室隔开;在茎的表皮下偶有与大型粘液细胞伴生的砂晶。花萼的表皮中偶有棱晶,花瓣表皮及雄蕊药隔中有砂晶;子房壁内表皮下一层细胞逐渐发育成含棱晶的连续细胞,同时子房维管组织中也形成大量棱晶。分析表明,结晶成分为草酸钙。     

Sedimentary history of Upper Silurian biostromes of Podolia (Ukraine) based on stromatoporoid morphometry

The sedimentary history of stromatoporoid biostromal accumulations reflecting various depositional conditions (autoparabiostromes and parabiostromes) is studied in two isochronous, Late Silurian carbonate sections of the Malynivtsy Formation from Podolia (western Ukraine, Kam'janec' Podil'skyj area). This study focuses on morphometrical analysis of massive stromatoporoids. Various stromatoporoid attributes, such as growth form, volume, surface character etc., are interpreted in terms of growth environments. Attributes of redeposited specimens are also analysed in terms of their susceptibility to exhumation and redeposition, and new criteria are presented in this matter. The exposed facies succession, which can be subdivided into three units: an oncolitic–fenestral complex and the stromatoporoid–coral complexes that underlie and cover it, represents the belt of shoals located at a considerable distance from shore, and its transition to a narrow zone of back-shoal tidal flats. The facies patterns proved to be strongly obscured by an intensive process of onshore redeposition of material during high energy episodes. These events caused exhumation and landward transport of stromatoporoids inhabiting soft-sediment bottoms of outer shelf areas, which were afterwards accumulated in parabiostromes in calm waters on lee side of a zone of shoals. The main process governing the distribution of redeposited stromatoporoids is fractional (weight) segregation. The high energetic events had less effect on stromatoporoid–coral autoparabiostromes that formed the zone of shoals, which were inhabited by stromatoporoids better adapted to permanent wave action, but nonetheless, they caused their partial reworking and depletion from those forms that did not resist redeposition, on one hand, and supplementation by specimens derived from offshore areas, on the other.     

Lack of latitudinal trends in wood anatomy of Dodonaea viscosa (Sapindaceae), a species with a worldwide distribution

Latitudinal or altitudinal variation in several anatomical characters of wood is common for woody dicotyledonous genera with a wide distribution, but whether such variation exists at the species level is disputed. Latitudinal and altitudinal trends in wood anatomy of Dodonaea viscosa were studied, using 102 samples collected between 41.2° S and 33.3° N latitude and 7-2750 m altitude. We studied variation in four quantitative features: vessel element length, fiber length, vessel frequency, and tangential vessel diameter. Ontogenetic trends were minimal with a slight decrease or increase in the innermost stem and were negligible among the studied specimens. Throughout the distributional range of the species, no latitudinal trends were detected in either the Northern or Southern Hemispheres. Altitudinal trends were also nonexistent, except for two features in specimens from China and Japan. Absence of latitudinal or altitudinal trends in this widely distributed species suggests that in some species the species-level variation in wood anatomy is not controlled by ecological gradients.     

两种类型栓皮栎软木细胞微观排列与形态特征

采用扫描电镜对秦岭北坡楼观台地区的厚皮、薄皮两种类型栓皮栎软木进行细胞微观构造观察分析,并与欧洲栓皮槠进行比较,以阐明厚皮、薄皮栓皮栎软木的相关特性,为中国栓皮栎软木的合理利用提供依据。结果表明:(1)两种类型栓皮栎软木细胞的排列结构较一致,均由内部中空的封闭型薄壁细胞紧密排列组成;在弦切面上呈蜂窝状排列,径切面和横切面上呈砖墙状排列;在径切面上,软木细胞侧高整齐地排列成行,且与树干轴向垂直;在横切面上,软木细胞侧高整齐地处于以树干轴为中心散发出来的射线上。(2)栓皮栎软木细胞大小、细胞壁和侧壁褶皱等受生长季节的影响;从软木细胞形态特征上看,厚皮类型软木细胞壁薄、细胞体积大,其软木质量优于薄皮类型。(3)与欧洲栓皮槠比较,发现厚皮类型栓皮栎早软木细胞棱柱高较小(20.6μm vs.(对比)30~40μm),软木细胞壁略厚(1.7μm vs.1~1.5μm),细胞实体积(细胞壁体积占细胞总体积比例)略大(18.75%vs.10%),厚皮类型栓皮栎软木比欧洲栓皮槠的软木质量差一些。(4)受树皮生长应力的影响,两种类型栓皮栎软木细胞侧高壁上多发生褶皱,早软木细胞褶皱严重,晚软木细胞没有褶皱,但在早晚软木交界或含有杂质处褶皱特别严重,表明厚皮类型软木细胞的侧壁褶皱程度高于薄皮类型。(5)对细胞形态特征及软木特性等的分析表明,薄皮类型栓皮栎软木质量比厚皮类型差,未来对软木资源的开发利用应更注重厚皮类型。     

Early symbiotic rugosan endobionts in stromatoporoids from the Rhuddanian of Estonia (Baltica)

The earliest known symbiotic rugosan endobionts occur in stromatoporoids from the early Rhuddanian of Estonia. The stromatoporoid Ecclimadictyon nikitini from the Tamsalu Formation contains the rugosan Donacophyllum middendorffii endobiont. A stromatoporoid Clathrodictyon boreale from the Varbola Formation contains Streptelasma estonica and Bodophyllum sp. endobionts. There are up to three endobiotic rugosans per stromatoporoid host. Stromatoporoid hosts were beneficial for symbiotic rugosans as elevated substrates on a seafloor that offered a higher tier for feeding; they also offered enhanced substrate stability. Stromatoporoids of the end‐Ordovician mass‐extinction recovery fauna hosted a diverse fauna of symbiotic endobionts. There were few if any negative effects of this mass extinction on the symbiotic endobionts.     

High-energy sedimentary events in lagoonal successions of the Upper Silurian of Podolia, Ukraine

Three Late Silurian carbonate profiles of the Malynivtsy and Skala Formations from Podolia (western Ukraine) are discussed in terms of sedimentation dynamics. Their common feature is the appearance of thick, stromatoporoid-rich beds within fine-grained peritidal deposits. These intercalations are composed of fossils typical of offshore sedimentary environments. In the most spectacular case, a channel, several tens of metres wide and infilled with stromatoporoids, is incised in a peritidal cyclic complex. The successions investigated exhibit sedimentary features that are diagnostic of onshore redeposition. Independently of the scale of the recorded sedimentary events, the onshore redeposition was caused by factors with energy levels exceeding those of average storms, probably by hurricanes or even tsunami waves. The dynamic nature of some of the stromatoporoid beds has to be taken into account when constructing the curves illustrating bathymetrical and facies development of the Silurian succession of Podolia. The genesis of lens-shaped stromatoporoid beds, elongated depending on their origin, either parallel or perpendicular to the facies belts, should be considered an important factor in reconstructions of the depositional architecture of sedimentary hydrocarbon collectors.     

Ensuring a representative sample of earlywood vessels for dendroecological studies: an example from two ring-porous species

The analysis of time series of wood cell anatomical features (such as the earlywood vessels of ring-porous trees) is a successful approach to understand the effect of environmental factors on tree growth and thus constitutes a valuable source of information about past environmental conditions. However, despite the rising interest in analyzing wood anatomical time series, little or no attention has been paid to establish an adequate sample of cells in order to minimize the risk of missing a valuable environmental signal. In order to contribute to such methodological bases, this paper is aimed at (1) identifying a representative sample of earlywood vessels within a tree, which encode the same climatic information, and (2) assessing if it is preferable to obtain the sample of vessels along one or two radii. Four individuals of sessile oak (Quercus petraea (Mattuschka) Liebl.) and sweet chestnut (Castanea sativa Mill.) were harvested and all their earlywood vessel lumina were measured along two 40-mm wide radial strips. Measured vessels were selected stepwise while increasing the tangential width of the wood section from 1 to 40 mm, analyzing at each step (1) the common signal of chronologies and (2) the correlation to the main climatic variables controlling growth. Additionally, both radii in each tree were analyzed together and separately. The results showed that a total tangential width of 10 mm was enough to stabilize the climatic signal with improvement when distributed along two different radii, but a slightly larger tangential width was required to reach an optimal common signal. We suggest that, at least for the case of these two species growing at this specific climatic context, two 5-mm increment cores ensure a representative vessel selection.     

Sedimentology and stromatoporoid palaeoecology of Frasnian (Upper Devonian) carbonate mounds in southern Belgium

Da Silva, A.‐C., Kershaw, S. & Boulvain, F. 2011: Sedimentology and stromatoporoid palaeoecology of Frasnian (Upper Devonian) carbonate mounds in southern Belgium. Lethaia, Vol. 44, pp. 255–274. Stromatoporoids are the most abundant large skeletal organisms in middle Frasnian carbonate mound environments of southern Belgium. They occur in environments ranging from flank and off‐mound, mound core, shallow mound and restricted mound. A detailed log and comprehensive sampling of stromatoporoids in a single section cutting through all middle Frasnian mound levels in La Boverie–Rochefort Quarry, near Rochefort and Dinant reveals a stromatoporoid assemblage comprising 10 genera; 472 samples, containing an overall total of 3079 stromatoporoids (including complete and fragmented specimens) have been studied. The following list gives abundance using numbers of specimens and areas of total stromatoporoid area on outcrop surfaces (% number; % area in cm²): Actinostroma (0.4; 9.2), Amphipora (15.5; 1.7), Atelodictyon (0.2; 4.4), Clathrocoilona (0.3; 0.5), Euryamphipora (13.7; 0.7), Idiostroma (2; 1.9), Salairella (1.2; 9.6), branching Stachyodes (43.2; 59.1), laminar Stachyodes australe (1.9; 1.3), Stictostroma (4.8; 13.1) and Trupetostroma (0.2; 0.8), showing that Stachyodes is approximately half of the total assemblage. Deeper environments contain more abundant low profile forms, shallow water facies contain more domical and bulbous forms; branching forms are ubiquitous. Low profile stromatoporoids are likely to have been important sediment stabilizers that may have led to expansion of the carbonate factory, and they may have therefore contributed to the structural building of the mounds. Stromatoporoid‐coral intergrowths are observed in only Stictostroma suggesting that there is a close biological relationship between them; however, stromatoporoid skeletons in almost all cases appear to be unaffected by the presence of intergrown corals, suggesting they were commensals. □Frasnian, Late Devonian, mounds, palaeoecology, stromatoporoid.     

The history and geography of diversification within the butterfly genus Lycaeides in North America

The Lycaeides butterfly species complex in North America consists of two nominal, morphologically defined species. These butterflies are ecologically diverse and appear to be distributed as a geographically complex mosaic of locally differentiated populations that may be undergoing adaptive radiation. We asked whether patterns of molecular genetic variation within the species complex are congruent with currently recognized morphological species and whether the distribution of molecular variation is consistent with the hypothesis that Pleistocene climate changes contributed to the process of differentiation within the genus. Variation in the form of the genitalia from 726 males from 59 populations clearly distinguishes both species with only six populations containing morphologically intermediate or ambiguous individuals. However, partitioning of molecular variance in a 236 bp section of the mitochondrial AT-rich region from 628 individuals (57 populations) surveyed using single strand conformation polymorphism analysis (SSCP) indicates that only 26% of the total genetic variation is distributed along nominal species boundaries as defined by morphology. Instead, three phylogeographical groups were detected, represented by three major haplotype clades, which account for 90% of the total genetic variance. Pleistocene glaciations appear to have fostered divergence during glacial maxima, while post-glacial range expansions created opportunities for gene exchange and reticulation along suture zones between geographical groups. Data presented here allow us to make inferences about the history of the species complex. However, evidence of ancestral polymorphism and reticulation limit our ability to define species boundaries based on mitochondrial DNA sequence variation.     

Improving the parameterization of stromatoporoid shapes – a detailed approach to stromatoporoid morphometry

Eight specimens of Devonian stromatoporoids with well visible latilaminae arrangement exposed on polished slabs were subjected to a detailed morphometric analysis. The studies have revealed that the so far used stromatoporoid parameterization method leaves a broad field of uncertainty concerning the exact definitions of particular parameters. The possible ways of making the measurements and the propositions of more precise definitions of the parameters used in the method, both of the growth form above the sea bottom and of the whole skeleton are therefore presented in this paper. The B_m - basal length of the skeleton, has been defined as a straight line joining the two ends of the basal surface, which have been pointed basing on the stromatoporoid's overall shape, latilaminae arrangement and angular relation to the main growth axis position in ontogenetical development, length. The B_n - basal length of the growth form above the sea bottom, is to be measured along a straight line joining the ends of the last visible latilamina. From among a number of possible definitions of the V_m - vertical height of the whole skeleton, a straight line joining the initial growth nucleus and the highest point on the specimen's surface above the B_m line has been selected. The V_n - vertical height of the growth form above the sea bottom is defined as the height of the point on the stromatoporoid surface highest above the B_n measured perpendicularly to it. A parameter of burial ratio, BR=(V_m-V_n)/V_m, is introduced.     

Stromatoporen aus dem Schwelmer Kalk (Givet) des Sauerlandes (Stromatoporen aus dem deutschen Paläozoikum 1)

A stromatoporoid fauna is described from the uttermost eastern quarry south of the Lenne river in Letmathe (Sauerland). The fauna consists of 8 species which have been found during a biostatistical study on the upper surface of a single limestone bed of Givetian age. The fauna can be interpreted as genuine community. — Most stromatoporoid species described from the German Paleozoic have been found in deposits of Eifelian, Givetian, and Frasnian age. The latest stromatoporoids found in the Rheinisches Schiefergebirge occur in biostromes of lowermost Tournai age near Aachen.