ALBERT

Description: SynopsisPast work on the genusPitusis reviewed and evidence adduced in favour of the view that it was a genus of arborescent Pteridosperms bearing the sterile bifurcate fronds known asLyginorachis papilioKidston. These probably resembledSphenopteris affinisL. & H. in the compression state. Fertile organs were probably borne on trifurcate fronds in which a stemlike median rachis (Tristichia ovensiLong) bore synangia (Telangiumsp.) composed of eight microsporangia, or alternatively seed-cupules ofStamnostoma huttonenseLong. Branching inPitusproduced single branches at a wide angle, or pseudo-whorls (close spirals) of about five branches. An anomalous ring of medullary xylem was sometimes associated with branching as inLyginopteris. This supports the view thatPitusshould be classified in the Lyginopteridaceae although it was arborescent and in some respects more advanced than many of the more shrub-like Pteridosperms.

Description: SynopsisThe limpet Acmaea virginea is an important agent of erosion of bivalve shells within the photic zone. This lower limit is governed by the depth range of shell-boring algae on which it feeds, the dominant alga being conchocelis. Any authigenic ferromanganese coatings on shells are removed by the grazing and the shells may become wafer thin and highly fragmented. The chiton Lepidopleurus also grazes shell surfaces but feeds more on superficial detritus than on the boring algae, and so its depth range is not so restricted. Both molluscs leave highly distinctive radula marks on shells which are potentially preservable in the fossil record. Acmaea virginea produces broad scoops, six-pronged, with very sharp narrow interstitial ridges. Lepidopleurus produces short, sharp scratches in sets of two, three or four, with wide interstitial ungrazed plateaux.The faecal pellets of both species contain 5–10 μm sized carbonate particles. Whereas there is little else in Acmaea pellets, which are white, cylindrical and only loosely held together, chiton pellets include much fine manganiferous material, detrital quartz and broken diatom frustules, and are well bound with mucilage which makes them dirty brown-grey in colour and ovoid. The data indicate that physical processes need no longer be assumed to be the major factor in the recycling of carbonate from shells, and in their fragmentation.

Description: SynopsisScottish streams of low sinuosity have four kinds of bars, three are bank-attached (lateral), and one is medial. Bar type is related to sinuosity, and as streams often increase in sinuosity away from source, there tends to be a variation in bar type successively downstream. The morphology and structure of the bars are related to grain size—gravel bars do not have the same bed forms and structures as those made of sand—and variations in flow stage. The bar head, composed mostly of gravel, forms during the high-flow stage, and as the flow falls so sediments of the lee face record the changing flow pattern. With further drop in water level the locus of sedimentation shifts to the bar tail where the dwindling flow may build diversely oriented bed forms and structures. Changes in the rate of fall, or differences in the maximum rise of water level, result in different proportions of sediment type being deposited.The mean orientation of the directional structures is not always alined with the mean stream direction, and the diversity of orientation is comparable with the diversity in orientation of directional structures in meandering streams. The variability in orientation is due to the effects of flood-produced bed forms in diverting the low-stage flow, stream sinuosity, and the changing orientation of the channel as it sweeps across the floodplain.

Description: SynopsisSix new specimens of petrified cupules ofHydraspermacf.tenuisfrom Oxroad Bay, East Lothian (Cementstone Group) have been examined. Sections of one show a close similarity in size and shape to compressed cupules ofSphenopteris bifidaL. and H. from the Lewis Burn (Scremerston Coal Group or lower Viséan) of Northumberland. The conclusion reached is that cupules ofHydraspermacf.tenuisLong are petrified equivalents of the compressed cupules ofSphenopteris bifidaL. and H. The morphological significance of this identification is discussed.

Description: 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.

Description: SynopsisRowleya trifurcata gen. et sp. nov. is described from specimens discovered in coal-balls from the Union Mine of Burnley, Lancashire. It consists of slender cylindrical axes (0·3–1·4 mm diam.) branched at long intervals by anisotomous dichotomies. Often three closely consecutive dichotomies produce a lateral trifurcation in which one or both outer branches have been arrested in growth. These bear one or two pairs of vascularised tapering appendages interpreted as ‘leaves’. Main axes usually possess a tetrarch solid strand of primary xylem somewhat like certain branches of Stauropteris. Slightly smaller axes often have a triarch strand of primary xylem triangular in cross-section. Backwardly directed branches are occasionally borne above a trifurcation and opposite a pair of ‘leaves’.Rowleya trifurcata is associated with Psalixochlaena cylindrica and Botryopteris hirsuta. Its closest affinities seem to be with Stauropteris and Psilotum.

Description: SynopsisNumerical taxonomic methods are applied to the Encrinurinae (Trilobita). Thirty-five cranidial and pygidial attributes are defined of which some (e.g. those relating to the glabellar tubercles) are specific to encrinurines and cybelines while others have application to non-encrinurids. Of nearly 200 named species of Encrinurinae only about one-third have been described in the literature in sufficient detail for their cranidial and pygidial attribute states be coded: a much smaller proportion of species is well enough known for librigenal, rostral, hypostomal and thoracic attributes to be coded. A comprehensive numerical taxonomy of the subfamily must therefore await detailed description of most of the known species. A list is given of encrinurine species in need of re-investigation. Meanwhile, 63 species can be coded for 34 attributes, and 75 species for 28 attributes. Principal components analysis is used to produce ordinations of these species. The minimal spanning tree superimposed on the ordination suggests possible evolutionary lineages. Ordination of the attributes is by non-linear mapping based on a distance matrix derived from the inter-attribute correlation matrix by the transformation (tanh−1 |r|)−1. The ordinations compare well with subjective assessments of relations and phylogenies.

Description: SynopsisDetailed mapping and accurate heighting reveal the extent of a well-preserved terrace system whose highest fragments lie c. 40 m above contemporary stream level. Kame terraces, pitted outwash terraces, terraces dissected by braided rivers and fan terraces are identified. The terrace fragments form a valley train whose uppermost levels were produced when glacier ice was still present in the glen. As successive streams readjusted to postglacial hydrological conditions, they excavated the valley fill of glacial deposits and carved out the terraces. It is inferred that subsequent stream discharges were generally smaller than those associated with deglaciation at the end of the period of ice sheet wastage. Areally extensive, heavily dissected, low level terraces are suggested to have been produced by meltwaters from a later deglaciation at the end of Zone III.

Description: SynopsisVarious types of trilobite exoskeletal sculpture are described and referred to a simple classification. Thin-section and surface examination of many such sculptural features shows them to be remnants of distinct cuticular organelles, which probably had a sensory function. The supposed sensory structures of well-preserved specimens of Phacops rana (Green) are described in detail and their presumed specific functions considered. Mapping sensilla distribution over the Phacops rana dorsal exoskeleton shows a distinctive pattern conveniently divisible into nine inferred sensory fields with the densest sensory concentrations on the head and margins of the dorsal shield.Conclusions on the importance of these sensory fields in mediating the trilobite's behaviour are combined with evidence from general morphology, palaeocology and evolutionary trends to suggest that Phacops rana was an active benthonic animal with a dual trophic capability lending considerable flexibility in adaptive radiation.The P. rana hypostomal suture, consisting of two short coplanar lateral branches, is described for the first time, indicating that the hypostoma had considerable freedom of movement, possibly connected with ingestion of bulky food.