Detailed descriptions and illustrations are presented of the structure of three representative species of tropical shipworms, Nausitora hedleyi, Teredo furcifera and Teredora princesae. The disposition of the various organ systems is described and illustrated with notes on the histology of the different regions so as to throw light on the adaptations and specializations of these unusual bivalves. The trend of evolution within the Teredinidae is discussed in the light of the available evidence contained in the present morphological studies.

A series of specimens from the Scottish Limestone Coal Group (Lower Namurian) is described, among which occurs Adelophthalmus cf. wilsoni (Woodward) from West Lothian, a group of specimens from the No. 2 Ironstone of Loanhead, Midlothian, one of which is recognized as belonging to the new species Mycterops (?) blairi, and a prosomal appendage from Lanarkshire which is referred to the genus Hibbertopterus. New evidence is presented on the nature of the prosomal appendages of Eurypterus (?) stevensoni R. Etheridge jr. which is designated the type species of the new genus Dunsopterus. The Coal Measures species Glyptoscorpius minutisculptus Peach is recognized as an eurypterid for which the new genus Vernonopterus is created. The systematics of these and other late palaeozoic genera which have been included by Kjellesvig-Waering (1966) in the families Woodwardopteridae and Hibbertopteridae are discussed.

A petrified lycopod found in a loose block of calciferous sandstone from the Cementstone Group in Berwickshire possesses a rooting stem-base similar to others previously assigned to Lepidodendron calamopsoides (Long 1964) but it shows continuity with a dichotomously branched stem about 15 cm. long, lacking leaves, but otherwise resembling Oxroadia gracilis (Alvin 1965). The diagnosis of Lepidodendron calamopsoides has been emended to include only axes bearing lepidodendroid leaf cushions as previously described. The new specimen, and others with like roots are tentatively assigned to Oxroadia gracilis Alvin.

Byne Hill, two miles south of Girvan, Ayrshire, is composed of Lower Ordovician igneous rocks which form partof the Girvan-Ballantrae igneous series. Byne Hill consists of serpentinized harzburgite, gabbro, diorite and trondhjemite which probably form a N.E.–S.W. elongated dome with trondhjemite occupying the core. There are transitional passages from gabbro into dioritic gabbro, diorite, quartz diorite and trondhjemite with no sharp contacts, and gabbroidal minerals and textures persist into the marginal hornblendic phases of the trondhjemite. The mineralogical changes are mainly progressive amphibolization and albitization of the gabbro accompanied by increases in SiO2 and Na2O. Geochemical culminations of FeO, MnO and P2O5 occur in the intermediate dioritic gabbro and diorites. Comparing the intermediate rocks with similar rock series from other areas suggests that mineralogical and chemical criteria do not always distinguish intermediate rocks of metasomatic origin from those produced by fractional crystallization. On Byne Hill the textural evidence suggests that the intermediate rocks are hybrids produced by reaction between crystalline gabbro and silicic sodium-rich solutions related to the trondhjemite, although there is evidence that the trondhjemite is itself metasomatic in origin. Serpentinization and rodingitization of the Byne Hill gabbro at contacts with serpentinite are described, and it is concluded that the gabbro was emplaced into the ultrabasic rocks prior to their serpentinization.

Cladoxylon waltoni sp. nov. is described from stems resembling C. radiatum Unger in the form of stele and absence of secondary xylem, but differing in the mode of emission of clepsydroid leaf-traces. Each leaf-trace originates as a band of xylem connecting two adjacent xylem arms. Dorsiventral axes with an ornate U-shaped bundle and 4-9 radiating arms are also included in the species. These give off alternate clepsydroid traces from two or three adjacent arms in a manner resembling a rachis. One specimen of Hierogramma mysticum Unger is described and three small rachides are interpreted as possible subdivisions of a Hierogramma frond.

Well preserved material of the crossopterygian fish Eusthenopteron enables fresh reconstructions and interpretations of its postcranial skeleton to be given. Comparisons throughout with other bony fishes show that it may be primitive in many features. Similarities with early amphibians such as the screw-shaped glenoid, the form of the humerus (on which an attempt to restore the pectoral musculature is based), the dorsal bicipital ribs and the possibility of a sacral attachment, throw much light on the origin of the tetrapod postcranial skeleton, particularly of the cheiropterygium. A functional analysis of the skeleton of Ensthenopteron is attempted, suggesting that it resembled the pike (Esox) in its mode of life and that it may have been capable of short journeys “walking” overland. The possible selective factors stimulating the evolution of such a fish, and further evolution to the tetrapod stage are discussed.

Descriptions are offered of two foetal gorillas representative of developmental stages intermediate between those previously described by Duckworth (1904), Schultz (1927) and Deniker (1885). They are numbered accordingly II and IV and comparison made throughout with the other stages represented in the literature.

Special attention has been paid to the ontogenetic changes occurring in the bodily form, and posture, cutaneous structures, cranial and skeletal development and in the disposition of the thoracic and abdominal viscera, much of which is previously known only in respect of Deniker's stage V.

Bohemian specimens of the phacopacean trilobites Reedops cephalotes (Hawle and Corda,) R. sternbergi (Hawle and Corda) and R. bronni (Barrande) have very well preserved schizochroal eyes. The sizes and distribution patterns of the eye lenses were studied and in R. sternbergi and R. bronni the angular bearings of all the lenses were measured, giving the visual range of the whole eye.

The internal anatomy of the eyes was also investigated, mainly from cut and polished sections. In many respects their morphology was comparable with that described previously in the Silurian and Devonian phacopaceans Phacops latifrons (Bronn) and Ananaspis communis (Barrande). The intralensar structures, however, are unlike those of P. latifrons and A. communis but bear a strong resemblance to the intralensar bowls of the Ordovician Zeliszkellinae, an early group believed to have been ancestral both to dalmanitaccan and post-Ordovician phacopacean stocks.

A brief history of the evolution of schizochroal eyes is given, some distinctive evolutionary trends are noted and the relationship of the structural pattern in Reedops is discussed with reference to that in other Phacopina.

Ovules of Eurystoma trigona sp. nov. are described. Over 330 unpollinated ovules were found attached to a petrified megasporophyll which appears to be a juvenile form of Alcicornopteris Kidston. Each ovule is triangular in cross section and has three wing-like extensions of the integument. None shows a female prothallus. The possibility that Alcicornopteris represents the fertile foliage of Stenomyelon is discussed.

In a previous paper (Andrews and Westoll 1970) the postcranial skeleton of the best known rhipidistian, Eusthenopteron, was described, and its bearing on the origin of the tetrapod postcranial skeleton discussed. The postcranial remains of other Rhipidistia are now described as far as they are known, and comparisons are made with Eusthenopteron and other forms where relevant. Possible modes of function are considered in relation to the habitats in which these fishes may have lived. These studies have made it necessary to revise rhipidistian classification; the Family Rhizodontidae is re-defined and placed alone in a third Order of Rhipidistia (the Rhizodontida, alongside the better known Osteolepidida and Holoptychiida). Fresh insight has been gained into the following morphological problems: the composition of the osteolepid ring-like centrum, the origin of the tetrapod scapular blade and the diphyletic origin of the tetrapods.

Three main stages are recognized in the evolution of the Scottish Caledonian orogen. Firstly, the development of the depositional framework from late Pre-Cambrian to early Ordovician times is outlined, The thick Moine and Dalradian sediments, accumulating on a continental rise, are shown to be equivalent to the shelf sequence of the foreland, and likely correlations are suggested. Secondly, the events comprising the Caledonian deformation and metamorphism of these sediments are reviewed and related to the development of a Benioff zone and coupled oceanic trench along the southern margin of the orogen through the Ballantrae complex. Comparison of stratigraphic and isotopic evidence for the age of these events leads to the conclusion that all major deformation and metamorphism occurred during a relatively short climactic episode 480–510 m.y. ago, within the Arenigian stage of the Ordovician. The third factor in the evolution of the orogen is post-climactic uplift and erosion continuing throughout Upper Ordovician, Silurian and Lower Devonian times. Contours of K–Ar mica ages are presented and related to the geological evidence for this prolonged period of isostatic recovery and thermal adjustment. The style and timing of granitic plutonism, which is closely associated with this third stage, may be indicative of crustal behaviour during uplift rather than continued metamorphism at depth.

The initial adaptive radiation of the Placodermi took place rapidly following the development of the basic placoderm adaptive complex after the ancestral scale covering of the trunk fused into a rigid shield, and not long before the group appears in the fossil record in the Lower Devonian. The radiation was mainly concerned with different ways of living in the benthos of a variety of marine and fresh-water environments; a few nektonic species appear late in the history of the Arthrodira. The fossil record shows the evolution of the orders in their adaptive zones. The zones become increasingly distinct as the orders evolve and become more specific in their adaptations, and the arthrodire, antiarch and rhenanid zones segregate into successively occupied sub-zones. The evolution of the Placodermi has been previously described in terms of improvements in the locomotor mechanism by an analysis of changes in the trunk-armour and pectoral fins. A more detailed description can be given by considering the feeding mechanism as well; this is particularly true of the largest order, the Arthrodira. Study of the feeding mechanism involves the cervical joints as well as the jaws and gnathals. The cervical joints had the same functions in feeding as the anterior part of the vertebral column (“the neck”) in many higher fish. In arthrodires jaw action involved vertical movements of the mandibular lever; the upper jaw apparatus is comparable to the rigid palatoquadrate-maxillary complex of primitive bony fish. The mandible was transformed into a bent lever in Brachyosteus by the development of a small “coronoid” process, but the arthrodire jaw apparatus remained undeveloped in comparison with Actinopterygii and Elasmobranchii. Arthrodire jaw suspension was autostylic. Evidence from the Rhenanida and Ptyctodontida has been interpreted to suggest that this condition was secondary, and that primitive placoderms had an elasmobranch or holocephalan-like palatoquadrate with hyostylic suspension. This view is not entirely supported by the state of the palatoquadrate in primitive arthrodires, but there is no good evidence that placoderms had a complete, open spiracular gill-slit (the aphethoyoid condition). Arthrodire phylogeny cannot yet be described in vertical lines, but four successive levels of organization of increasing efficiency can be recognized; the actinolepid, phlyctaenaspid, coccosteomorph and pachyosteomorph levels. These levels can be defined by simple characters relating to broad adaptations in the locomotor and feeding mechanisms. Evolutionary trends in the Arthrodira include the enlargement of the scapulocoracoid and base of the pectoral fin and the reduction of the spinal plate and flank armour, as the fish gain better control in the water and more myomeres become available for use in swimming; and the enlargement of the nuchal gap and development of the cranio-thoracic joint as powerful muscles are developed to raise the head to give a wide gape, accompanied by the specialization of the gnathals for different modes of feeding. Some of these trends are reversed in compressed, nektonic species. The description of arthrodire phylogeny in terms of changes that can be understood from a functional point of view reveals interesting examples of mosaic and parallel evolution. Parabelosteus n.gen. is erected.

The adaptive character and possible course of evolution—following permanent byssal attachment—of the heteromyarian form in the Bivalvia is considered in relation to the eulamellibranch Dreissenacea and the filibranch Mytilacea. In both it assumes the extreme condition of ventral (anterior) flattening representing a high degree of adaptation for epifaunal life. The presence of a shell shelf in the umbonal regions of Dreissena and Septifer is associated with the greatest degree of ventral flattening; it permits retention of the anterior adductor and its attachment to parallel surfaces. Enlargement of the posterior regions of the visceropedal mass and the posterior territory of the mantle/shell involves formation of an elongated opisthodetic ligament. That of the Dreissenacea, here initially described, is of unique complication. In primitive infaunal isomyarians an organ of locomotion through soft substrates, in these heteromyarians the foot becomes essentially concerned with byssal attachment with which much the greatest part of the small anterior and large posterior retractors becomes exclusively concerned. Although strikingly similar to the Mytilacea, the Dreissenacea which now inhabit slowly moving or still, silt-laden freshwaters would seem most probably to have evolved under very different marine conditions prior to their relatively recent migration into freshwaters.

It is confirmed that the type species of the genus Glyptoscorpius Peach 1882 is a subjective synonym of Adelophthalmus Jordan and Meyer 1854. Species which have been referred to Glyptoscorpius are reviewed and their present taxonomic position defined. Cyrtoctenus gen. nov., type species Cyrtoctenus peachi sp. nov., is designated to accommodate forms bearing five pairs of specialised abdominal appendages of which the first is comb-like. Four species of Cyrtoctenus from Devonian and Carboniferous rocks in Scotland, England, Belgium and Czechoslovakia are recognized. The structure and affinities of these forms are discussed with special reference to the comb-like appendages and their ornamentation in relation to these features in other arthropods. In particular the development of filaments and fulcra from different types of scales is discussed. The characters of the new genus are found to be so distinctive as to require the creation of the new order Cyrtoctenida for its accommodation.