The first part of the present thesis consists of a brief survey of previous research on the subject and sets out the objectives, terminology and methodology followed in the study. The second part is entirely devoted to a monographic description of the Early Jurassic articulate brachiopod faunas of three key areas, providing in most cases photographic illustrations for the first time. A major chapter dealing vdth Argentina is based upon the author's personal sampling from the Provinces of San Juan, Mendoza and Neuqudn in the Argentine Andes, and supplemented by museum collections from these and additional areas. About thirty taxa are described, among them six new species, three new subspecies and one new terebratulid genus (Peristerothyrie). It is the first time that South American Mesozoic brachiopods have been investigated with the help of serial grinding techniques to reveal their internal structures. In another chapter the brachiopod assemblages from the islands of Timor and Seram (Indonesian Archipelago) are revised on the basis of museum collections and published data. A reappraisal of twenty-seven taxes reported previously has revealed the existence of several subjective q'nonyms, one homonym -thioh had to be renamed- and several genera are recorded for the first time from that area. The next chapter provides further new records of many genera which have been recognized in a reassessment of museum collections from western Greece and an examination of undescribed material from east-central Greece. The whole assemblage comprises more then thirty taxes, including a new species. In the third part of the thesis the new evidence provided by the systematic studies is combined with a review of the relevant literature and the patterns of distribution of most known genera are analysed on a world-wide scale. A series of forty-seven maps displaying the occurrences as compiled, supports the distinction of the following kinds of distribution: Pandemic, Borealoid, Boreal, Sub-boreal, Tetbyoid, Meaogeal, Sub-mesogeal and Pacificoid.

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The revision of Early Jurassic monotacean, pectinacean and plicatulacean bivalves is based on museum material and own collections from 50 localities in the provinces of San Juan, Mendoza and Neuqué in western Argentina. Twenty-four species belonging to 17 genera of the families Monotidae, Oxytomidae, Asoellidae, Propeamussiidae, Entoliidae, Pectinidae, Terquemidae, Plicatulidae, Placunopsidae and Dimyidae are systematically described. The new pectinid genus <i>Agerchlamys</i> and new species of <i>Kolymonectes, Entolium</i> and <i>Terquemia</i> are proposed. All other species are referred to previously known taxa. Placement of genus <i>Kolymonectes</i> in the family Propeamussiidae is supported by evidence of an outer prismatic calcitic shell layer and lack of ctenolium. Further, a close relationship of <i>Radulonectites</i> to <i>Camptonectes</i> is revealed. The subgenus <i>Harpax</i> is re-validated and distinguished from <i>Plicatula</i> s.s. by differences in hinge, ligament and relative convexity of valves. Ten of the taxa are referred to species which have an almost cosmopolitan distribution. The others belong to distinct South Pacific stocks, some of which were previously thought to be typical to Boreal regions, but which have a bipolar distribution. <i>Palmoxytoma, Kolymonectes, Radulonectites, Agerchlamys</i> and the group of <i>Plicatula (Harpax) raps</i> Bayle & Coquand characterize an Early Jurassic Austral Realm. Along the East Pacific, the boundaries between Austral and Tethyan Realms lie in the Andean region. A biostratigraphical zonation of the Argentinian Lower Jurassic based on pectinaceans is discussed, including five Assemblage Zones which can be recognized in Argentina and Chile. These are named after local species of mainly circum-Pacific genera, such as <i>Otapiria, Radulonectites</i> and <i>Posidonotis</i>. Their equivalence with other local biostratigraphic units is analysed and their correlation with other biostratigraphical schemes based on bivalves from other circum-Pacific regions is attempted.

The sedimentological and foraminiferal content of gravity cores collected from the continental shelf and upper slope off the Niger delta, West Africa, have been studied. Careful study of the cored sediments has allowed the identification of characteristics which distinguish exposed sediments which are partly or wholly relict in composition from deduced non-relict (modern) sediments. The faunal content of modern sediments has been compared with the known oceanographic conditions, and the identified qualitative relationships have been shown to be useful for palaeoenvironmental interpretation. The depth distributions of the modern faunae appear to be largely influenced by temperature, and faunal breaks have been found to correlate with the upper and lower limit of the regional thermocline. Species which are apparently endemic to the Gulf of Guinea and West Africa are largely confined to the near-surface water and species characteristic of the upper and middle slope are generally widespread geographically. Relict sediments exposed near the shelf edge are characterized by Amphistegina gib-bosa which is not believed to be living in the modern Gulf of Guinea. The disappearance of A. gib-bosa appears to correlate with an increase in freshwater discharge of the Niger distributaries soon after 11,500 B.P. The more recent relict faunae are similar to the present and apparently document the rise in sea level. There is no evidence that any of the cored sediment was deposited in an environment other than an exposed shelf.

A broad study of the Conulariida reveals many unresolved issues regarding their palaeobiology and systematics. Evidence previously cited in support of a scyphozoan affinity is found to be inconclusive; suggested close affinities with other groups such as annelids and molluscs are also rejected. It seems preferable to consider conulariids as an extinct group of phylum status. The structure and composition of the conulariid shell is investigated and discussed in a functional context. The phosphatic conulariid shell is usually thin (possibly because of the environmental scarcity of phosphate) with a large organic component (probably from biomechanical constraint). A mantle-type secretory regime for the conulariid shell is proposed. This and various microstructural features of the shell seem to argue against a cnidarin affinity. The conulariid shell has features in common with the skeletons of brachiopods, molluscs and conodonts although a close affinity with any of these groups is probably unlikely. Patterns of conulariid distribution and abundance are analysed. A recurrent theme appears to be the occurrence of abundant conulariids in unusual sedimentary settings associated with low diversity benthic faunas. A pelagic mode of life for some conulariids remains a possibility although a benthic, upright, sessile lifestyle for the majority of conulariid taxa seems most likely. The apical diaphragm is not interpreted in terms of a mode of life transition but as a taphonomic feature resulting from an originally fragile septate shell. A systematic revision of the Conulariida allows a tentative phylogeny to be proposed together with a new classification. The Conulata, comprising the single order Conulariida, are elevated to phylum status, <i>Stenothecopsis</i> and <i>Glyptoconularia</i> are given subfamilial status, with <i>Conchopeltis</i> and <i>Sphenothallus</i> removed from the Conulata. The following new taxa are described; <i>Exoconularia</i> sp. nov. a., <i>Pseudoconularia</i> sp. nov. a. and <i>Paraconularia crustula</i> var. nov. a.

Little is known about how patterns of deep-sea community structure, but diversity in particular, vary with depth. There are two competing theories in the literature. The first suggests that diversity shows no decline with depth, while the second proposes a more complex pattern in which diversity increases with depth reaching a peak between 2000-3000m. It was decided to test which of these theories most appropriately described polychaete diversity patterns in the Rockall Trough. Spade box core samples were analysed from two transects; one which ran from 400 to 1061m and the second which ran from 1000-2900m, and also from five replicate samples on the floor of the Trough. The processes underlying diversity patterns were also investigated and compared to other studies using a conceptual model. The results of this investigation found that polychaete species richness increased with depth, reaching maximum values between 1000-1400m. Analysis of equitability indicated that the upper slope stations were highly dominated, but gradually became more equitable with increasing depth, although there was considerable variation. There was no evidence to support the role of competition or intra-taxocene predation as structuring processes. However, there was support for the role of disturbance in the form of near-bed currents in structuring upper slope assemblages. In particular, it appeared to be the frequency of high speed currents which was important. Analysis of species distributions indicated that species turnover was highest in areas where the frequency of high speed currents was greatest. By contrast, trophic groups did not show any major trends. Rockall Trough abundances were lower than other studies from the world ocean but no explanation can be offered to explain this. By contrast, species richness and number of species was as high as comparable regions. It was suggested that this maybe related to the disturbance regime in the Trough.

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