Because of fundamental differences between trace fossils and body fossils, ichnologic nomenclature is beset with difficulties. Foremost is inconsistent treatment by the International Commission on Zoological Nomenclature (lack of sanction for post-1930 names, confusion over the "rule of priority") and inadequate curation of type specimens. However, ichnologists have contributed their own problems via inadequate diagnoses and descriptions, misconceptions of ichnologic and taxonomic principles, proliferation of names and failure to engage in true monographic revisions. All these difficulties are illustrated in a thorough reevaluation of the ichnogenera Planolites Nicholson and Palaeophycus Hall. Contrary to a popular but ill-founded scheme in which these ichnogenera are differentiated simply on the presence or absence of branches, Planolites is an unlined burrow infilled with sediments having textural and fabricational characters unlike those of the host rock, whereas Palaeophycus is a lined burrow filled with sediments typically identical to those of the surrounding matrix. Planolites represents active backfilling of sediment in an ephemeral burrow constructed by a mobile deposit feeder and Palaeophycus represents passive sedimentation within an open dwelling burrow constructed by a predaceous or suspension-feeding animal. In addition to ichnological nomenclature and ethology, the ramifications are important in paleoecology, sedimentology and diagenetic studies. Currently recognized ichnospecies of Planolites include P. montanus Richter, P. beverleyensis (Billings) and P. annularis Walcott. Those of Palaeophycus include P. heberti (Saporta), P. tubularis Hall, P. striatus Hall, P. sulcatus (Miller and Dyer) and P. alternatus n. ichnosp.

Trace fossil nomenclature and the Planolites-Palaeophycus dilemma

Many problems—from soil research to ceramics—require a reliable characterization of the clay minerals involved. This can be done using four clay-organic reactions: (i) staining tests and dye adsorption; (ii) glycerol and glycol adsorption; (iii) intercalation; (iv) alkylammonium ion exchange. Dye adsorption (staining tests) and glycerol adsorption allow a preliminary identification of the clay mineral groups. Intercalation reactions indicate minute differences between kaolins which cannot be detected by XRD and DTA. Alkylammonium ion exchange provides the best method for characterizing smectites and is sensitive to changes in the layer charge.

Characterization of clays by organic compounds

Interlayer and Intercalation Complexes of Clay Minerals

This study reviews published information on Mugil cephalus from around the world, with recent genetic studies indicating that the flathead mullet may indeed be a species complex. Disciplines that are covered range from the taxonomy, genetics and systematics, through a variety of biological and ecological attributes, to biomarker and fisheries studies. The eurytopic nature of M. cephalus is emphasized, with the migratory life history covering a succession of very different aquatic environments (e.g. rivers, estuaries, coastal lakes/lagoons, marine littoral, open ocean), each of which is occupied for varying lengths of time, depending on the population characteristics within a region and the life-history stage of the species. Interpretation of these movements over time has been greatly enhanced by the use of otolith micro-chemistry which has enabled scientists to map out the different habitats occupied by individual fish at the different life stages. The range of physico-chemical attributes within these environments necessitates a wide tolerance to differing conditions, especially with regard to salinity, turbidity, dissolved oxygen and temperature, all of which are discussed in this review. The importance of M. cephalus to the ecological functioning of coastal systems is emphasized, as well as the pivotal role that this species fulfills in fisheries in some parts of the world. The parasites range from internal trematode and cestode infestations, to external branchyuran and copepod parasites, which use M. cephalus as either an intermediate or final host. The value of the flathead mullet as a biomarker for the monitoring of the health of coastal habitats is discussed, as well as its potential as an indicator or sentinel species for certain ecosystems.

A global review of the cosmopolitan flathead mullet Mugil cephalus Linnaeus 1758 (Teleostei: Mugilidae), with emphasis on the biology, genetics, ecology and fisheries aspects of this apparent species complex

Kaolin and Serpentine Group Minerals

Variations in differential thermal analysis curves of siderite

Alteration of Clay Minerals by Digestive Processes of Marine Organisms.

Spray drying dilute suspensions of bentonitic montmorillonite produces a powder that shows totally random orientation of the crystallites within a sample large enough to diffract X-rays. The powder is collected by an electrostatic precipitator and can be handled in the normal mounting processes without introducing preferred orientation. Electron micrographs show this powder to be composed on a small scale of thin, crumpled, and rolled films. The extremely small montmorillonite crystallites that make up the film are oriented with [001] directions perpendicular to the film surface. Orientation within the plane of the film is random as shown by selected area electron diffraction. Crumpling and rolling of the film is sufficient to make the orientation of [001] directions random in three dimensions in a large sample when X-ray diffraction is registered. The X-ray diffraction patterns all show diffraction maxima (both hk and 00l), and their relative intensities with respect to each other can be determined. The line broadening of the 06 and the 003 peaks was studied. The average crystallite size as calculated from the line broadening varied from six to eleven unit layers thick for four bentonitic montmorillonites. The average lateral dimension of crystallites varied from 140 A to 250 A. Ratios of lateral dimensions to thickness varied from 2.3 to 3.4.

Size and Shape of Montmorillonite Crystallites

Samples from kaolin deposits in the Dry Branch, Georgia, area were examined in’ oriented thin section, by X-ray diffraction, and as carefully disaggregated sand-sized grains The object was to determine the orientation of kaolinite crystals with respect to any gross stratification in the deposits and with respect to their mineral precursors

Petrology of the Dry Branch, Georgia, Kaolin Deposits

A sodium-saturated Texas bentonite was fractionated into six particle-size ranges. The expansion of each fraction was observed by X-ray diffraction under controlled humidity conditions ranging from 0–100 per cent r.h. At all humidities, the fine fractions expanded more than the coarse. A single size fraction expands through a series 10 A, 12.4 A and 15.5 A. The expansion from 10–12.4 A occurs at progressively lower relative humidities for smaller size fractions in the same way as the expansion from 12.4–15.5 A. The gradation from high resistance to expansion in the coarse fractions to low resistance to expansion in the fine fractions appears to be continuous.

Edward C. Jonas

Papers

Variations in differential thermal analysis curves of siderite

Alteration of Clay Minerals by Digestive Processes of Marine Organisms.

Size and Shape of Montmorillonite Crystallites

Petrology of the Dry Branch, Georgia, Kaolin Deposits

Structural Charge Density as Indicated by Montmorillonite Hydration