Feeding ecology of the gulf silverside,Menidia peninsulae,near Crystal River,Florida, with notes on its life history

Feeding habits ofMenidia peninsulae were analyzed monthly over a one year period and compared to planktonic prey available at the capture site. Three feeding stages were found: (1) In early spring, young-of-the-year fed on tychoplankton and detritus. (2) From late spring through winter,M. peninsulae preyed selectively on calanoid copepods and cypris larvae. (3) GravidM. peninsulae fed primarily on amphipods and larval silversides. In the Crystal River area,M. peninsulae reproduce in early spring. Silversides apparently migrate from the higher salinity bays to the lower salinity marshes in the summer, and then move back into the bays in fall.     

Summer meroplanktonic prosobranch larvae occurring off Beaufort,North Carolina

The occurrence of planktonic prosobranch larvae identified during the summers of 1977, 1979 and 1981 off Beaufort, North Carolina is given. Forty-two species were recorded; 29 of these were found each summer. Observations and identifications were made on 12 newly described larvae: Lacuna sp, Epitonium sp. 1 (apiculatum), Epitonium sp. 2, Strombus alatus, Erato maugeriae, Simnia acicularis, Natica sp. 1, Natica sp, 2, Natica sp. 3, Natica sp. 4, Olivella adelae, Mangelia sp. and Sp.? Turridae. A key for the identification of planktonic prosobranch veligers occuring in summer months is included.     

Life history of the spotfin killifish,fundulus luciae (pisces: cyprinodontidae), in Fox Creek Marsh,Virginia

Fundulus luciae was collected for a year at Fox Creek Marsh and, occasionally, at other salt marshes along the York River, Virginia. It occurred in high intertidal areas in brackish, sometimes oxygen deficient shallow ditches, mudholes and tidal rivulets located in stands ofSpartina alterniflora. Preserved specimens were examined to determine the reproductive season, fecundity, diet and associated metazoan parasites of the species. Developing ova were present from mid-April to mid-August and exhibited a broad size range; the number of large ova (>1.6 mm diameter) never exceeded 16 per female. Stomach contents consisted mainly of detritus, diatoms, ostracods, dipterans and copepods. All major metazoan parasite groups except Cestoda were represented onF. luciae; Monogenea were most numerous, with 57.2% incidence. Eggs and larvae were described. Preserved larvae ofF. luciae were distinguished from those ofF. heteroclitus by their dorsal pigmentation pattern. It was concluded thatF. luciae, a purportedly rare species, is not rare, but probably restricted to high intertidal salt marshes where it may have been previously overlooked.     

Larval settlement behavior in the jellyfishAurelia aurita (Linnaeus) (Scyphozoa: Semaeostomeae)

The distribution of sessile marine invertebrates is often the consequence of the selection of a suitable substrate by motile larvae. Motile planulae larvae ofAurelia aurita (Linnaeus) are exposed to an artificial substrate in the laboratory to determine if they possess the capacity both for specific orientation and for discrimination of surface texture at time of attachment. More than 90% (P<0.001) of the planulae fasten to the underside of objects. As a result, developing scyphistomae hang with the oral surface downward as commonly encountered in the field. The effect of surface texture on planula attachment is equivocal; this may reflect an indifference to surface texture, a limited capacity to locomote across rough substrate, or a mechanism of response sensitive only to large surface irregularities. These results are compared with those obtained for the planulae ofCyanea capillata (Linnaeus). The planular effected orientation of the scyphistoma may be generally true for coastal representatives of the Semaeostomeae, and perhaps for other shallow water Scyphozoa (including the Class Cubozoa).     

Phylogenetic Problems in Polynesian Simuliidae (Diptera: Culicomorpha): A progress report

As a basis for eventual control of the vicious anthropophilic and ornithophilic simuliid females of the Marquesas Islands, a taxonomic revision of Polynesian Simuliidae is in progress. Cytotaxonomic studies reveal two simuliid species in Rarotonga, Cook Islands; nine species in Tahiti, Society Islands, and two in the Marquesas Islands. A cytophylogeny is now available. Polynesian Simuliidae are unique in possessing heterogametic females. A reconstructed phylogeny, based mainly on morphological character states of larvae and pupae, agrees well with the cytophylogeny. One of the new species which is closely related to Simulium oviceps Edwards has larvae with highly reduced, non-functional cephalic fans. Ages of the Polynesian islands are discussed in relation to possible dispersal of Simuliidae into Polynesia.     

Sensitivity of early life stages of blueback herring to moderate acidity and aluminum in soft freshwater

The sensitivity of the blueback herringAlosa aestivalis to acidity and aluminum (AI) in reconstituted, soft freshwater (23–25 mg I^?1 hardness as CaCO₃) was investigated in a continuous exposure laboratory study. Mature (20–24 h postfertilization) embryos were more tolerant than 1- to 5-day-old yolk-sac larvae. Significant mortality of embryos occurred only when pH was 5.0 and the total Al concentration was 0.42 mg I^?1 (predicted MIBK-extracted total monomeric AI=0.34 mgI^?1). Moderate acidity dramatically decreased the survival of yolksac larvae. Mean mortality was 99% in pH 5.0 and 89% in pH 5.7 compared to 38% in pH 6.5 and 16% in pH 7.8 without AI. The toxicity of AI to yolk-sac larvae was pH- and dose-dependent. Total AI concentrations up to 0.34 mg l^?1 (predicted total monomeric AI up to 0.21 mg l^?1) were not toxic at pH 6.5 and 7.8. At pH 5.0 and 5.7, AI increased the rate at which yolk-sac larvae died during a 96-h exposure (i.e., time to 50% mortality decreased with increasing AI). Continuous exposure to a predicted total monomeric AI level of only 0.03 mg I^?1 at pH 5.0 killed all yolk-sac larvae in <24 hours. The mechanisms of acid and AI toxicity were apparently physiological and not associated with extensive cellular damage. Acidification events measured in Chesapeake Bay tributaries may reduce survival of blueback herring yolk-sac larvae and embryos exposed to those events.     

Synthetic Mn3+-kyanite and viridine, (Al2-xMn x 3+ ) SiO5, in the system Al2O3-MnO-MnO2-SiO2

Experiments on the join Al₂SiO₅-“Mn₂SiO₅” of the system Al₂O₃-SiO₂-MnO-MnO₂ in the pressure/temperature range 10–20 kb/900–1050° C with gem quality andalusite, Mn₂O₃, and high purity SiO₂ as starting materials and using /_O2-buffer techniques to preserve the Mn³⁺ oxidation state had following results: At 20 kb/1000°C orange-yellow kyanite mixed crystals are formed. The kyanite solid solubility is limited at about (Al_1.88Mn _0.12 ³⁺ )SiO₅ and, thus, equals approximately that on the join Al₂SiO₅-“Fe₂SiO₅” (Langer and Frentrup, 1973) indicating that there is no Jahn-Teller stabilisation of Mn³⁺ in the kyanite matrix. 5 mole % substitution causes the kyanite lattice constants a _o, b _o, c _o, and V _o to increase by 0.015, 0.009, 0.014 Å, and 1.6 ų, resp., while α, β, γ, remain unchanged. Between 10 and 18 kb/900°C, Mn³⁺-substituted, strongly pleochroitic (emeraldgreen-yellow) andalusite_ss (viridine) was obtained. At 15 kb/900°C, the viridine compositional range is about (Al_1.86Mn _0.14 ³⁺ )SiO₅-(Al_1.56Mn _0,44 ³⁺ )SiO₅. Thus, Al→Mn³⁺ substitutional degrees are appreciably higher in andalusite than in kyanite, proving a strong Jahn-Teller effect of Mn³⁺ in the andalusite structure, which stabilises this structure type at the expense of kyanite and sillimanite and, thus, enlarges its PT-stability range extremely. 17 mole % substitution cause the andalusite constants a _o, b _o, c _o, and V _o to increase by 0.118, 0.029, 0.047 Å and 9.4 ų, resp. At “Mn₂SiO₅”-contents smaller than about 7 mole %, viridine coexists with Mn-poor kyanite. At “Mn₂SiO₅”-concentrations higher than the maximum kyanite or viridine miscibility, braunite (tetragonal, ideal formula Mn²⁺Mn³⁺[O₈/Si0₄]), pyrolusite and SiO₂ were found to coexist with the Mn³⁺-saturated ky _ss or and _ss, respectively. In both cases, braunites were Al-substituted (about 1 Al for 1 Mn³⁺). Pure synthetic braunites had the lattice constants a _o 9.425, c _o, 18.700 Å, V _o 1661.1 ų (ideal compn.) and a _o 9.374, c _o 18.593 ų, V _o 1633.6 ų (1 Al for 1 Mn³⁺). Stable coexistence of the Mn²⁺-bearing phase braunite with the Mn⁴⁺-bearing phase pyrolusite was proved by runs in the limiting system MnO-MnO₂-SiO₂.     

Preliminary studies of food habits of juvenile fish,China Poot Marsh and Potter Marsh,Alaska, 1978

During the year 1978, juvenile salmonids were collected from coastal streams running through China Poot Marsh and the stomach contents analyzed. Stomach contents of threespine stickleback (Gasterosteus aculeatus) and staghorn sculpin (Leptocottus armatus) from China Poot and of threespine stickleback from Potter Marsh were also analyzed; these two species were generally caught in tidal pools on the marshes. The juvenile coho salmon (Oncorhynchus kisutch) had the most varied diet; 37 different prey items were identified in the stomachs. By comparison, 25, 26, and 33 prey taxa were identified in the stomach contents of Dolly Varden char (Salvelinus malma), threespine stickleback, and staghorn sculpin, respectively. Amphipods were the dominant prey of all fish collected from China Poot Marsh; chironomidae larvae were the most common item in the stomach contents of threespine stickleback from Potter Marsh. The diets of all species changed over the course of the study period; the change was most dramatic for juvenile salmonids and sculpins.     

Modern diversity of the macroalgae of the Sea of Azov,the Black Sea,and the Caspian Sea

Currently, the species list of the macroalgae (excluding Charales) inhabiting the southern seas of Russia includes 388 species, specifically, 362 species in the Black Sea, 46 species in the Sea of Azov, and 70 species in the Caspian Sea. The species list has been increased by approximately 30% (96 species, most of them are registered in the Black Sea), compared to the data obtained 30 years ago. The green and red macroalgae of warm-water Mediterranean and tropical origin (Ceramium, Polysiphonia, Laurencia, Ulva, and Chaetomorpha) and brown algae (Sargassum and Cytoseira) were the key invaders. Nowadays the maximal species diversity is found on the Crimean coast and the Turkish coast of the Black Sea; and the species list of the Turkish coast differs significantly from all the other studied sites of the Black Sea. The number of the algae of the warm-water complex increased the most in 1990s–2000s in the Black Sea; species of boreal-tropical and subtropical origin dominate. However, such a tendency was not observed in the Sea of Azov and in the Caspian Sea, but expansion of the habitats of the brackish green algae has been registered.     

Radiation resistant of native Deinococcus spp. isolated from the Lout desert of Iran “the hottest place on Earth”

Two native ionizing radiation-resistant bacteria were isolated and identified from a soil sample collected from extreme conditions of the Lout desert in Iran. The hottest land surface temperature has been recorded in the Lout desert from 2004 to 2009. Also, it is categorized as a hyper arid place. Both ionizing radiation and desiccation may cause damage on genome. Soil sample was irradiated in order to eliminate sensitive bacteria then cultured in one-tenth-strength tryptic soy broth medium. Bacterial suspension used for radiation treatment. Morphological and physiological characterization and phylogenetic studies based on 16S rRNA gene sequence were used for identification. The cells were rod shape, non-motile, non-spore forming and gram positive. The 16S rRNA gene sequence showed 99.5 % of similarity to Deinococcus ficus. Phylogenetic dendrogram demonstrated that the isolates branched with D. xibeiensis, D. ficus and D. mumbaiensis. Both isolates were resistant to >15 kGy of gamma radiation and >600 J m² of UV radiation. This is the first report on radiation resistant bacteria belonging to genus Deinococcus isolated from the Lout desert of Iran.     

X-ray and HRTEM study of sursassite: Crystal structure,stacking disorder,and sursassite-pumpellyite intergrowth

Sursassite is monoclinic, space group P2 ₁/m, a=8.70, b=5.79, c=9.78 Å, β=108.9°. The crystal structure was determined with X-rays and refined to R=0.065, obtaining Mn₂Al₃[(OH)₃(SiO₄)(Si₂O₇)] as ideal crystal chemical formula. Sursassite, isostructural with macfallite Ca₂Mn₃[(OH)₃(SiO₄)(Si₂O₇)], is closely related to pumpellyite Ca₂Al₃[(OH)₃(SiO₄)(Si₂O₇)]. In fact both sursassite and pumpellyite, apart from the different chemical composition, are built up by common structural layers, which are repeated by different stacking vectors. As a result, faulted stacking sequences are energetically possible. Examination by high resolution transmission electron microscopy (HRTEM) shows that frequent (001) pumpellyite-like lamellae are intergrown with thicker (001) sursassite lamellae. Usually, the guest lamellae are a few unit cells thick along [001] and continuous along the (001) plane, although also rare interrupted lamellae are found.     

The lattice energy of forsterite. Charge distribution and formation enthalpy of the SiO 4 4− ion

In the lattice energy expression of forsterite, based on a Born-Mayer (electrostatic+repulsive+dispersive) potential, the oxygen charge z _o, the hardness parameter ρ and the repulsive radii r _Mg and r _Si appear as unknown parameters. These were determined by calculating the first and second partial derivatives of the energy with respect to the cell edges, and equalizing them to quantities related to the crystal elastic constants; the overdetermined system of equations was solved numerically, minimizing the root-mean-square deviation. To test the results obtained, the SiO ₄ ^4? ion was assumed to move in the unit-cell, and the least-energy configuration was sought and compared with the experimental one. By combining the two methods, the optimum set of parameters was: z _o=?1.34, ρ=0.27 Å, r _Mg=0.72 Å, r _Si=0.64 Å. The values ?8565.12 and ?8927.28 kJ mol^?1 were obtained, respectively, for the lattice energy E _Land for its ionic component E _L ⁰ ,which accounts for interactions between Mg²⁺ and SiO ₄ ^4? ions only. The charge distribution calculated on the SiO ₄ ^4? ion was discussed and compared with other results. Using appropriate thermochemical cycles, the formation enthalpy and the binding energy of SiO ₄ ^4? were estimated to be: ΔH _f(SiO ₄ ^4? )=2117.6 and E(SiO ₄ ^4? )=708.6 kJ mol^?1, respectively.     

The geochemistry of pyroxenes from the lower layered series of the Jimberlana intrusion,Western Australia

Most of the Al³⁺ entering the pyroxenes does so by substituting for tetrahedral Si⁴⁺. This creates a charge imbalance that requires the simultaneous entry of Cr³⁺, Ti⁴⁺, Fe³⁺ or Al³⁺ into octahedral sites. Cr³⁺, because of its high crystal field stabilisation energy (CFSE), is the most important of these elements to enter the early-formed pyrosenes but it is replaced by Ti⁴⁺ later in fractionation when the Cr³⁺ content of the melt becomes depleted. The dependence of Cr³⁺ and Ti⁴⁺ on charge balance controls their partition between coexisting pyroxenes and olivines. Ca-rich pyroxene which contains more Al³⁺ than Ca-poor pyroxene also has more Ti⁴⁺ and Cr³⁺ whereas olivine, which contains negligible Al³⁺, has low Cr³⁺ and Ti⁴⁺. The Al³⁺ content of pyroxenes is influenced by changes in P, T, \(a_{{\text{SiO}}_{\text{2}} }\) and \(a_{{\text{Al}}_{\text{2}} {\text{O}}_{\text{3}} }\) of the magma and by the nature of the ion providing charge balance in the octahedral site. Of these \(a_{{\text{SiO}}_{\text{2}} }\) is dominant and variations in the Al³⁺ content of the Jimberlana pyroxenes correspond closely with the expected changes in the \(a_{{\text{SiO}}_{\text{2}} }\) of the melt. The substitution of divalent ions, such as Mn²⁺ and Ni²⁺, in the pyroxene lattice is by replacement of Fe²⁺ or Mg²⁺ in the octahedral M ₃ and M ₂ sites and is therefore independent of charge balance. If there are no size restrictions, the principal factor to be considered is the CFSE the ion receives in octahedral co-ordination. Ni²⁺, which receives a high CFSE, partitions strongly between the early-formed pyroxenes and olivines and therefore becomes depleted in the magma with fractionation. Conversely Mn²⁺, which receives zero CFSE, concentrates in the magma with fractionation and becomes a more important substitute in the later-formed pyroxenes. Its geochemical behaviour is controlled by its size. The narrow miscibility gap of the Jimberlana pyroxenes and the high En content of the Ca-poor pyroxenes at the bronzite pigeonite changeover suggest that these pyroxenes crystallised at a higher temperature than pyroxenes of comparable composition from other intrusions.     

A model of the OH positions in olivine,derived from infrared-spectroscopic investigations

Polarized infrared (IR) spectroscopy of olivine crystals from Zabargad, Red Sea shows the existence of four pleochroic absorption bands at 3,590, 3,570, 3,520 and 3,230 cm^?1, and of one non pleochroic band at 3,400 cm^?1. The bands are assigned to OH stretching frequencies. Transmission electron microscopy (TEM) shows no oriented intergrowths in this olivine; it is concluded that OH is structural. On the basis of the pleochroic scheme of the absorption spectra it is proposed that [□O(OH)₃] and [□O₂(OH)₂] tetrahedra occur as structural elements, assuming that the vacancies are on Si sites. If M2 site vacancies were assumed [SiO₃(OH)] and [SiO₂(OH)₂] tetrahedra occur as structural elements.     

Development of an empirical model for rainfall-induced hillside vulnerability assessment: a case study on Chen-Yu-Lan watershed,Nantou, Taiwan

In Taiwan, the hillside is about 70 % of total area. These areas also have steep topography and geological vulnerability. When an event of torrential rain comes during a typhoon, the landslide disasters usually occur at these areas due to the long duration and high intensity of rainfall. Therefore, a design which considers the potential landslide has become an important issue in Taiwan. In this study, a temporal characteristic of landslide fragility curve (LFC) was developed, based on the geomorphological and vegetation factors using landslides at the Chen-Yu-Lan watershed in Taiwan, during Typhoon Sinlaku (September 2008) and Typhoon Morakot (August 2009). This study addressed an effective landslide hazard assessment process, linking together the post-landslide damage and post-rainfall data for LFC model. The Kriging method was used to interpolate the rainfall indices (R ₀, R, I) for numerical analysis. Remote sensing data from SPOT images were applied to analyze the landslide ratio and vegetation conditions. The 40-m digital elevation model was used for slope variation analysis in the watershed, and the maximum likelihood estimate was conducted to determine the mean and standard deviation parameters of the proposed empirical LFC model. This empirical model can express the probability of exceeding a damage state for a certain classification (or conditions) of landslides by considering a specific hazard index for a given event. Finally, the vulnerability functions can be used to assess the loss from landslides, and, in the future, to manage the risk of debris flow in the watershed.     

High temperature solvent growth of anorthite on the join CaAl2Si2O8-SiO2

Stoichiometric anorthite, CaAl₂Si₂O₈, Pˉ1, with sharp a, b, c, and d diffractions was grown, using a CaV₂O₆ solvent, by cooling at 2 ° C per hour from 1450 to 750 ° C in air. Euhedral crystals up to 5 × 3× 0.5 mm, with prominent {010} and well-developed {110} and {001}, were obtained by spontaneous nucleation. Nonstoichiometric anorthite with excess SiO₂ (CaAl₂Si₂O₈+Si₂Si₂O₈) was grown on the join CaAl₂Si₂O₈-SiO₂. Chemical analysis of the synthetic anorthite, having the highest SiO₂ content, with maximum vacancies on M-site gave □_0.110 Na_0.006Ca_0.884Al_1.80Si_2.20O₈, and X-ray diffraction showed a trend from stoichiometric Pˉ1 through diffuse Pˉ1 to body-centered Iˉ1 probably reflecting increasing disorder caused by a higher Si/Al ratio in the T-sites and the positional disorder accompanied by M-site vancancies. Annealing of the nonstoichiometric diffuse Iˉ1 anorthite in air at 1050 ° C for 14 days resulted in exsolution of minute SiO₂ inclusions due to probable ordering in the T-sites and filling of M-sites by Ca. Stoichiometric Pˉ1 anorthite was not obtained by annealing at 1050 ° due to appreciable solubility of SiO₂ in CaAl₂Si₂O₈. Metastable hexagonal CaAl₂Si₂O₈ was found to be a twinned monoclinic crystal with cell dimensions: a = 10.24 (2), b = 17.74 (3), c= 14.99 (5) ?, β = 92.05 (5) °, space group C2.     

Temporal and spatial patterns in abundance and diversity of fish assemblages in Elkhorn Slough,California

Assemblages of ichthyofauna of shallow inshore habitats along Californía’s central coast are described in terms of species composition, abundance, and life-style categories. A total of 22,334 fishes from 65 species and 27 families was collected with otter trawls at six sites in the main channel and tidal creeks of Elkhorn Slough, a tidal embayment and seasonal estuary, and two nearshore ocean stations in Monterey Bay during 44 months between August 1974 and June 1980. Greater than 90% of the catch comprised 10 species. The four dominant species,Cymatogaster aggregata, Leptocottus armatus, Phanerodon furcatus, andEmbiotoca jacksoni, occurred during most or all seasons and were classified as residents or partial residents. Several abundant species were marine immigrants that seasonally use the slough as spawning and nursery grounds; this resulted in higher abundance and species richness during summer. Species collected during winter largely were slough residents. Species compsosition and richness varied with distance from the slough entrance. The ocean assemblage was most different, and its similarity to other stations decreased progressively with distance inland and into the tidal creeks. During our study, 5,074 fishes were collected by beach seine in Bennett Slough, a remote shallow marsh basin adjacent to the entrance of Elkhorn Slough. Species richness was relatively low and three euryhaline species accounted for >80% of the total catch. The species assemblage was most similar to those at the tidal creek and most shallow stations of Elkhorn Slough. Resident species numerically dominated assemblages in Bennett Slough and the most inland areas of Elkhorn Slough. The high relative abundance of marine-related fishes (classified as marine, marine immigrant, and partial resident), entering Elkhorn Slough early in life or as spawning adults indicates the importance of this habitat to nearshore fish assemblages.     

Upper temperature tolerance of spot,Leiostomus xanthurus,from the cape Fear River estuary,North Carolina

The temperature tolerance and resistance times of postlarval (<25 mm SL) and small juvenile spot,Leiostomus xanthurus, from the Cape Fear Estuary, North Carolina were tested in the laboratory. Critical thermal maximum techniques were used to determine first equilibrium loss (FEL) and critical thermal maximum (CTM) end points and thermal shock methods were used to determine 96-h upper incipient lethal temperatures (LT₅₀). Acclimation temperatures ranged from 10 to 35°C and acclimation salinities were 10, 20 and 30‰. A quadratics model was fit to the CTM and FEL data; r² values were 0.924 and 0.928 respectively. Acclimation salinity, estimated weight, acclimation salinity by acclimation temperature interaction and acclimation temperature by estimated weight interaction were the significant components of the CTM model. Predicted CTM values ranged from 30°C at 10 °C and 30‰ acclimation to just over 40°C at 30 °C and 30‰ acclimation. Acclimation temperature, acclimation temperature squared, estimated weight and acclimation temperatures by estimated weight interaction were the significant components of the FEL model. Predicted FEL values ranged from around 28°C at 10°C and 10‰ acclimation to about 39°C at 30°C and 30‰ acclimation. The 96-h LT₅₀ values of spot acclimated to 20‰ increased linearly with acclimation temperature to 25°C. From about 25 to 35°C, LT₅₀ values increased very little with acclimation temperature. The ultimate upper incipient lethal temperature of postlarval and small juvenile spot was estimated at 35.2°C. Increased salinity increased resistance time but decreased LT₅₀ estimates. Thermal shock tests were better for predicting the effects of thermal addition than were CTM tests.     

Seasonal and spatial distribution of cumaceans in the Mobile Bay estuarine system,Alabama

Seasonal occurrence patterns within the Mobile Bay estuary, Alabama, of five species of cumaceans are described.Oxyurostylis smithi was most abundant, followed byLeucon americanus, Cyclaspis varians, Eudorella monodon andAlmyracuma proximoculi. With the exception of the oligohalineA. proximoculi, the cumaceans encountered within the estuary are euryhaline marine species that are most abundant at the lower bay stations and that utilize the estuary only when environmental conditions are favorable.     

Magnetic structure and cation distribution in (Fe,Mn)2SiO4 (olivine) by neutron diffraction

The cation distribution in the synthetic samples of olivine-type structure with composition (Fe _x Mn_1?x )₂SiO₄ was determined at room temperature and confirms previous Mössbauer results. At low temperature an antiferromagnetic ordering is observed. The magnetic structures can be described in the crystallographic cell (i.e. k=0). They are interpreted on the basis of the irreducible representations (modes) of the symmetry groups which are compatible with Pnma. The dominant modes observed for all compounds, including Fe₂SiO₄ and Mn₂SiO₄, only differ in their direction. The main direction of magnetization is dominated by the Fe²⁺ single-ion anisotropy. At 4.2K, for x=0.29, it is parallel to the c-axis, whereas for x=0.76 the direction is parallel to the b-axis. The anisotropy of the M1-sites dominates in the first case, whereas M2-anisotropy dominates in the second case. The influence of temperature is demonstrated for x=0.50 where c is the main direction at 4.2K, when it is b at 38K.