The genus Sphenothallus was erected by Hall (1847, p. 261), who originally considered it a land plant. Sphenothallus was later classified as a marine invertebrate. Moore and Harrington (1956, p. F65) regarded Sphenothallus as a hydrozoan or scyphozoan. Van Iten et al. (1992, p. 139) supported Moore and Harrington's idea, and argued that it displays a close relationship to conularids (also see Li, 2000, p. 91). However, Mason and Yochelson (1985, p. 93–94) suggested that Sphenothallus is an annelid or “worm” (also see Fauchald et al., 1986, p. 64; Feldmann et al., 1986, p. 344–345; Choi, 1990, p. 403; Bartels et al., 1998, p. 114–117). The exact phylogenetic affinity of Sphenothallus is still debated.

John K. Page, Chief of the Production Section of the Zoological Record has kindly informed us (personal commun., 16 November 1998) that the generic name Tetraloba Alvarez, Rong, and Boucot, 1998 (Brachiopoda: Athyridida) (Alvarez et al., 1998, p. 843) is preoccupied by an insect (Collembola) genus published by Lee, 1983. According to Article 60 of the ICZN rules, we here propose Quadriloba (from the Latin, quattuor, four and lobus, a rounded projection or protuberance) as replacement name for Tetraloba Alvarez, Rong, and Boucot, 1998, not Tetraloba Lee, 1983.

While preparing materials for the pentameroid portion of the Treatise on Invertebrate Paleontology revision of the brachiopod volumes, problems were encountered with four enigmatic genera: Rugolepyros Lenz, 1989; Aenigmastrophia Boucot, 1971; Spondylostrophia Kulkov, 1967; and Stricklandistrophia Sapelnikov and Rukavishnikova, 1975.

Restudy of two Early Silurian (Aeronian) stricklandioid species, Stricklandinia transversa Grabau, 1925 and Stricklandiella robusta Rong and Yang, 1981 from the Yichang area of South China, leads to the recognition of two new genera, Sinokulumbella and Sinostricklandiella. Two types of spondylia and four types of cardinalia are recognized for the Stricklandioidea and can be used for classification of the superfamily at the generic or even familial level. On the basis of these characters, five groups (typified by Stricklandia, Stricklandiella, Kulumbella, Microcardinalia, and Aenigmastrophia) can be recognized within the superfamily. Sinokulumbella n. gen., with a small, shallow, bowl-shaped spondylium and a pair of outer hinge plates that are discrete from the crura, is regarded to be affiliated with the Kulumbella group. Sinostricklandiella n. gen. has superimposed plicae and costae, although its internal structures are similar to the Stricklandiella group. A revised classification of stricklandioids implies that the Chinese pentamerides were characterized by strong provincialism during the early and middle Llandovery. This interpretation is supported further by the complete lack of true Stricklandia and Microcardinalia lineages in South China. Different stocks of stricklandioids in Baltica, Laurentia, South China, Siberia, and Kazakhstan may have experienced allopatric evolution, punctuated by several pulses of faunal migration or exchange between these paleoplates during the Llandovery. Evolution of the Stricklandia lineage is significantly different from that of Kulumbella and Sinokulumbella, particularly in that the outer plates disappeared earlier in the kulumbellids than in the stricklandiids.

Reexamination of type and topotype material revealed the presence of well-developed ventral and dorsal interareas in two virgianid brachiopods from South China, Eoconchidium jiangshanensis Liang (in Liu et al., 1983) and Paraconchidium shiqianensis Rong, Xu, and Yang, 1974, of Late Ordovician and Early Silurian ages, respectively. A cladistic analysis of the common virgianid taxa, incorporating new data on the development of interareas, confirms Paraconchidium Rong, Xu, and Yang, 1974 as a valid genus (not a junior synonym of Pseudoconchidium Nikiforova and Sapelnikov, 1971) and warrants E. jiangshanensis as the type species of Deloprosopus new genus (not allied to either Eoconchidium or Tcherskidium as previously believed). Our preliminary survey on the suborder Pentameridina, based on available material or illustrations of well-preserved, disarticulated (typically silicified) valves, indicates that 1) the interareas are more commonly developed in the superfamily Pentameroidea than was reported previously, especially in the families Virgianidae and Subrianidae; 2) the ventral and dorsal interareas commonly do not occur as paired planar surfaces in the Pentameroidea, as they do in the superfamily Stricklandioidea; and 3) despite the common absence of a ventral interarea, the development of a sharply delimited dorsal interarea appears to be ubiquitous in the Pentameroidea and possibly in the suborder Pentameridina. In the currently adopted classification, the presence of matching ventral and dorsal interareas is treated as one of the diagnostic characters that separate Stricklandioidea from other superfamilies of the Pentameridina. The new data presented herein on the development of interareas imply the need to reevaluate the taxonomic and evolutionary significance of the ventral and dorsal interareas, pending a thorough survey on their distribution in the suborder Pentameridina.

The brachiopod genus Dicoelosia is generally considered a typical deep-water taxon. New data suggest that some species of the genus may have invaded relatively shallow-water habitats during its geological history. However, there is scant evidence for its invasion of shallow-water environments after the terminal Ordovician mass extinction. Dicoelosia occurs in the shallower-water benthic shelly assemblages of the lower Niuchang Formation (upper Rhuddanian, Llandovery) of Meitan County, northern Guizhou Province, South China. Evidence of a move to shallow water includes its morphology and population structure, regional paleogeography, sedimentology, together with the abundance and diversity of its shallow-water associates. Following the biotic crisis, deep-water environments were barely habitable, and may have driven Dicoelosia into shallower-water niches. The taxon endured the less suitable shallow-water environments until the deep-water benthic zones ameliorated after the recovery, implying a shallow-water refugium existed after the biotic crisis. A new species Dicoelosia cathaysiensis is erected herein. There is only one record of this genus in South China and this unique occurrence may reflect the distinctive paleobiogeography and environments of this region.

Proconchidium brodeurensis n. sp. occurs 212 m above the base of member B of the Baillarge Formation on Brodeur Peninsula, Baffin Island, 8 m below the Ordovician–Silurian boundary. Study of Proconchidium shows that it can be easily distinguished from Eoconchidium but possesses many characters that are similar to those in Tcherskidium. Analysis of internal structures suggests that the three genera can be distinguished from each other and belong to Virgianidae. Tcherskidiidae is a synonym of Virgianidae and should be abandoned.

This represents the first recorded occurrence of Proconchidium in North America. Although this genus and its related genera Tcherskidium Sapelnikov, 1972, and Eoconchidium Rozman, 1967, are common in Ashgill strata of Eurasia, they have not been recorded or illustrated from North America. This led to the suggestion that distinct brachiopod biogeographic provinces may have existed during the Ashgill. The occurrence of these genera probably indicates that they may have lived in mostly tropical and subtropical zones.

Eospirifer praecursor n. sp. is the oldest known eospiriferine, probably ancestral to the entire Spirifer group. It is described here based on external and internal mold material from the uppermost part of the Changwu Formation (mid-Ashgill, Late Ordovician), Hejiashan, Jiangshan, western Zhejiang, East China. A study of the ontogeny of E. praecursor n. sp. suggests that the cardinalia of early growth stages are more similar to those of early atrypoids rather than to those of the orthoids but the brachidia in these earliest Eospirifer are still unknown. The possibility that eospiriferines were derived from an atrypoid stock cannot be excluded. All early eospiriferine species recorded from the Ashgill, Rhuddanian, and early Aeronian are reviewed for comparison. Their morphological diversification reveals early evolutionary experimentation. Based on the Ashgill occurrence of Eospirifer, it is likely that East Asia may be considered as one of the eospiriferine source areas.

Holorhynchus giganteus Kiaer, 1902, a common Late Ordovician (mid-Ashgill) pentameride brachiopod in the Baltic region, Kazakhstan, and southern Tien Shan, is documented for the first time from the Badanjilin Formation (mid-Ashgill) of western Inner Mongolia (Alxa block), North China. Serial sections of the Chinese material confirm the presence of a vestigial ventral median septum in the early growth stage of H. giganteus, but the septum becomes embedded in the secondary shell thickening at the adult growth stage. A survey of the type material from Norway and additional material from other regions indicates that the incipient ventral median septum is a much more commonly developed structure than was previously believed. The presence of a well-developed pseudodeltidium in the Tien Shan material of H. giganteus and the absence of such a structure in conspecific material from many other regions require a systematic revision of the generic group. Holorhynchus has rodlike crura (=brachial processes) that do not form flanges at their junctions with the inner hinge plates (=outer plates = crural plates) and outer hinge plates (inner plates). This, together with the development of a crude spondylial comb structure, points to its affinity to the Virgianidae rather than to the Stricklandiidae. Holorhynchus can be regarded as a Lazarus taxon because of its absence during the crisis (Hirnantian) and survival (early-middle Rhuddanian) intervals associated with the Late Ordovician mass extinction and its reappearance in Kazakhstan and North China during the Early Silurian (late Rhuddanian-early Aeronian). The mid-Ashgill Holorhynchus fauna, typified by a number of large-shelled pentamerides, was common in the Baltic region, the Urals, Kazakhstan, Tien Shan, Alxa, Qaidam, Kolyma, and east-central Alaska, but largely absent from Laurentia and Siberia (except for Taimyr) in the ancient tropical-subtropical regions. This paleobiogeographic pattern agrees with the general pattern of the Late Ordovician brachiopod provincialism.

A review of the Late Ordovician, chiefly mid-Ashgillian, to Early Silurian, Llandoverian, pentameroidean brachiopods, the Virgianidae, permits them to be assigned to three subfamilies (Virgianinae [10 genera assigned], Mariannaellinae [5 genera assigned], Pleurodiinae [2 genera assigned]). Diagnoses are presented for each subfamily, with comments on diagnostic characters for each genus and species. All the genera occur in what are interpreted to have been relatively low latitude, warm water environments in Arctic North America, northern Europe, northern Asia, central Asia and South China; the presence of Australian Ordovician virgianids is uncertain at this time. The mid-Ashgillian pentameroid adaptive radiation was followed by latest Ordovician mass extinction, subsequently surviving recovery and radiation in the middle-Late Llandovery. Silurian radiations convergently mimicked the Ordovician event in many respects.

Phylogenetic relationships among higher taxa of articulate brachiopods that developed a spiralium as mineralized support for the lophophore, and the resulting classifications, are not universally agreed upon due to the complex pattern of character evolution within the phylum. Our results, using phylogenetic methodology in conjunction with traditional methods, showed a more complete and easily testable picture of this evolution than either method used alone. A detailed working hypothesis of athyridide phylogeny and the supporting evidence on character distribution is given, and a new classification of the impunctate and punctate athyrids sensu lato is presented with diagnoses to subfamily. Agreement between the stratigraphical first appearance of athyridid subfamilies and their cladistic rank was quite good (except for the koninckinoids), suggesting that both outgroup and traditional paleontological methods indicate a similar direction of character polarity in the evolution of the group. The classification is proposed based on a mix of external and internal characters which persisted during unbroken lineages. New taxa are the families Parazygidae and Triathyrididae; the subfamilies Whitfieldellinae, Triathyridinae, Septathyridinae, Cleiothyridininae, Ochotathyridinae and Plectospirinae, and the genera Brimethyris, Carteridina, Tetraloba and Cooperispira. We studied the great morphological diversity among the athyridids. Their complete stratigraphical ranges help in building phyletic lineages.

A silicified brachiopod assemblage living between the first and second episodes of latest Ordovician mass extinction is first described from micritic bioclastic limestone of Kuanyinchiao Bed, northwestern Guizhou, southwest China. It contains six species, Dalmanella testudinaria (Dalman, 1828), Plectothyrella crassicosta (Dalman, 1828), Hindella crassa incipiens (Williams, 1951), Eostropheodonta sp., the characteristic constituents of the Hirnantia fauna, and two new species, Fardenia modica and Dorytreta longicrura. It lacks Hirnantia, Kinnella, Cliftonia, and Paromalomena, the other characteristic elements of the Hirnantia fauna. A new, low diversity community (inner BA3) dominated by brachiopods is proposed as the Dalmanella testudinaria-Dorytreta longicrura Community along with the trilobite Dalmanitina nanchengensis Lu, rugose corals, and gastropods. Composition of this community of the Hirnantia fauna was controlled primarily by temperature, water depth, and substrate. Comparison with other communities of the Hirnantia fauna in south China supports this conclusion. Fluctuations in generic composition of the Hirnantia fauna and the related factors are also discussed.

“Lingulepis’ malongensis Rong from the upper part of the Lower Cambrian Chiungchussu Formation of Yunnan is referred to Lingulellotreta Koneva; L. malongensis (=Lingulellotreta ergalievi Koneva) is redescribed on the basis of new material from the Lower Cambrian of south Kazakhstan. It is the earliest known taxon of the Lingulellotretidae, which is unique within the Linguloidea in having an elongate pedicle foramen and internal pedicle tube. The occurrence of Lingulellotreta malongensis in south China is considered usually to be of Atdabanian age, but brachiopod based correlation with south Kazakhstan suggests that a possible Botomian or younger age, for both the upper part of Chiungchussu Formation in Yunnan and the lowermost part of Shabakty Group in the Malyi Karatau Range, is equally plausible.

Storeacolumnella hudsonensis is described as a new genus and species of encrusting, colonial organism that lived in an intertidal, rocky-shore environment. The fossil was discovered in the basal beds of the Upper Ordovician Port Nelson Formation at a coastal outcrop on Hudson Bay near Churchill, Manitoba. Showing some possible characteristics of sponges and other possible characteristics of calcaerous green algae, this matlike organism is considered nonetheless to have uncertain taxonomic affinities. It consists of cylinder-shaped columns, each with an internal system of star-shaped filaments or spicules as viewed in transverse section. The cylinders stand vertical in longitudinal section and are densely packed together to form a mat. The hard substrate to which the mat is attached consists of a boulder eroded from the Precambrian Churchill Quartzite. Maximum colony size observed in a single example exhibits a diameter of not less than 80 mm and maximum thickness of 5.85 mm.

The only published δ13C data from the Ordovician of China are from the Lower and Upper Ordovician, and only the latter records include a significant excursion, namely the Hirnantian excursion (HICE). Our recent chemostratigraphic work on the Upper Ordovician (Sandbian–Katian) Pagoda and Yanwashan formations at several localities on the Yangtze Platform and Chiangnan (Jiangnan) slope belt has resulted in the recognition of a positive δ13C excursion that has values of ~+1.5‰ above baseline values. This excursion starts a few metres above a stratigraphic interval with B. alobatus Subzone conodonts as well as graptolites of the N. gracilis Zone. The distinctive conodonts Amorphognathus aff. Am. ventilatus and Hamarodus europaeus first occur at, or very near, the excursion interval. Because these conodonts appear in the stratigraphic interval of the Guttenberg δ13C excursion (GICE) in Estonia, we identify the Chinese excursion as the GICE. This is the first record of the GICE in the entire Asian continent. It confirms that GICE is a global excursion and provides an illustration of how δ13C chemostratigraphy, combined with new biostratigraphic data, solves the problem of the previously controversial age of the Pagoda Formation and how this classical stratigraphic unit correlates with the Baltoscandian and North American successions.

Earliest Silurian (basal Llandovery) brachiopod faunas are surveyed and listed from around the globe, and divided between Lower Rhuddanian and Upper Rhuddanian occurrences. 60 genera are known from the Lower Rhuddanian within 20 superfamilies and there are 87 genera in 25 superfamilies in the Upper Rhuddanian. The 29 areas surveyed span the globe, both latitudinally and longitudinally. Only six superfamilies are Lazarus taxa which are known both from the Ordovician and Middle Llandovery (Aeronian) and later rocks but have not been recorded from the Rhuddanian. These are surprising results, since many previous studies have inferred that the Rhuddanian was a time of very sparse faunas. The global warming that followed the latest Ordovician (Hirnantian) ice age did not proceed quickly, with an ice-cap probably present through at least the Llandovery. There is a marked absence of Lower Rhuddanian bioherms even at low palaeolatitudes; however, the ecological recovery rate was far faster than that following the end-Permian mass extinction event. The partitioning of the Rhuddanian shelf faunas into well-defined benthic assemblages progressed slowly over the interval.

A new genus of pentameride brachiopod, Costilamnulella, described herein from the middle Ashgill of Sweden, is particularly interesting in that the ventral valve possesses both an interarea and a palintrope. Brachiopods normally have one or the other, but both structures do occur amongst the pentamerides, e.g. in Clorinda, Anastrophia and Brevilamnulella. The presence of these structures in three separate pentameride families indicates the persistence of the more primitive condition of an interarea whilst the more advanced palintrope is becoming established. Costilamnulella is interpreted as a restricted side line of the main development of the more widely occurring Brevilamnulella, which survived the end-Ordovician event and may have shared its ancestry with the ubiquitous Clorinda.