SynopsisEurypterids of the Superfamily Stylonuroidea Diener 1924 sensu Størmer (1974, 373) from the Pentland Hills, Midlothian, are redescribed and the evidence which these forms may give concerning the life environment of the Gutterford Burn Eurypterid Bed (Upper Llandovery), from which most of them have been obtained, is considered. Five species are recognised. Parastylonurus ornatus (Laurie) is redescribed with special reference to the organs of locomotion and reproduction. A new form from the Gutterford Burn is described as Parastylonurus hendersoni sp. nov. Stylonurus macrophthalmus Laurie is designated the type species of the new genus Hardieopterus and Stylonurus knoxae Lamont as the type species of the new genus Lamontopterus. The unique holotype of Lamontopterus knoxae is of morphological interest in showing evidence of the gut.Stylonuroids from other Scottish Silurian localities are also considered. Two new species, Brachyopterella ritchiei sp. nov. from Seggholm and Hardieopterus (?) lanarki sp. nov. from the Logan Water are described. Stylonurella spinipes (Page) is redescribed and this species is reported for the first time from Seggholm.The new information provided by this study has raised a number of problems of classification and the criteria upon which eurypterids are classified, and particularly those applied to the stylonuroid eurypterids, are re-assessed and a new classification of the Stylonuroidea proposed. This has required the description of new taxa; a new family, the Parastylonuridae, is proposed to accommodate Parastylonurus, Hardieopterus and probably Lamontopterus which share a unique combination of characters of the prosomal appendages and metastoma. A new genus, Kiaeropterus, is described to accommodate certain species previously assigned to Stylonurella but displaced from that genus as now emended.A reconstruction of Parastylonurus ornatus in the walking position is attempted and has resulted in the recognition of a new generation of problems related to the functional morphology of these animals. Criteria which may appropriately be used in deciding the manner in which they walked and the posture which they adopted when doing so, are discussed. It is suggested that, in response to certain anatomical and physiological constraints which otherwise would have rendered the animals unstable in the walking position, the post-abdomen and telson have been specialised as hydrodynamic structures for monitoring water movements and vectoring the animal for maximum walking efficiency. The significance of this hypothesis is discussed in relation to the functional morphology and evolution of other members of the Stylonuroidea.

Cyrtoctenus wittebergensis sp. nov. is described from a unique holotype from the Witteberg Group of the Cape Supergroup. It is a giant hibbertopteroid eurypterid having combs and specialised movable spines of crytoctenid type (Størmer & Waterston 1968) on the more distal podomeres of the second to fourth prosomal appendages. The function of the combs and their associated movable spines is discussed and it is suggested that together they formed a unique adaptation of eurypterid structures to sweep filter-feeding, the combs forming the filters and the spines the cleaners. The digestive tract is remarkably preserved and shows a spiral valve, posterior to the stomach, which is interpreted as an adaptive feature in this large arthropod to increase the absorptive area of the gut.The new evidence provided by the South African specimen has required the re-interpretation of the disarticulated Cyrtoctenus specimens previously described from Europe. Disjecta membra recently obtained from the Tournaisian of Foulden, Berwickshire, which may belong to Cyrtoctenus, are described and show characters previously unknown in Scottish material but similar to certain features in the South African specimen.The taxonomic relationships within the Hibbertopteroidea are discussed in the light of the new combination of characters found in C. wittebergensis. Two families are recognised in the superfamily, the Hibbertopteridae, including Hibbertopterus and Campylocephalus, and the new family Cyrtoctenidae which is here erected to include Cyrtoctenus, Dunsopterus and possibly also Hastimima.

SynopsisWith the exception of Pterygotus rhenaniœ Jaekel, for which the new genus Jœkelopterus is proposed, the published accounts of the median abdominal appendages of the Pterygotidæ are inadequate. An examination of the British material was undertaken with a view to improving our knowledge of the opercular anatomy of the family. An account is given of the genital appendages associated with both sexes of Erettopterus bilobus (Salter) and Pterygotus anglicus Agassiz, of the Baltic species Erettopterus osiliensis (Schmidt) and of British forms in which only one type of appendage is known. Attention has been given also to the cheliceræ of the British type species because of the importance which has been attached to this character in classification. The significance of the chelate and genital appendages in the classification and biology of the Pterygotidæ is discussed.

SYNOPSISLOWER Carboniferous eurypterids are rare, and consequently the Scottish eurypterid fauna ie of importance, in a world setting, because of the number of species of that age which it contains. Since the Scottish forms were originally described, great advances have been made in our knowledge of the Eurypterida which have made necessary the present critical re-examination of all available Scottish Carboniferous eurypterid specimens. Five species, belonging to four genera, are described and illustrated. Fresh evidence of the anatomy of Campylocephalus scouleri (Hibbert) is presented and the wider issues of eurypterid morphology raised by homology with this specialised species are discussed. C O N T E N T S PAGE

SynopsisIt 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.