A number of European species of the genus Arrenurus (Acari, Hydrachnellae) are revised. The following synonyms are established: A. hofsteni Walter and A. sinuator commutatus Viets as junior synonyms of A. latus Barrois & Moniez; A. ornatulus Viets of A. compactus Piersig; A. walteri Koenike of A. neumani Piersig; A. cyanipes (Lucas) sensu Walter and A. bucharicus Sokolow of A. papillator (Müller); A. stjoerdalensis naias Lundblad of A. coronator Thor; A. eugeminus Piersig and A. imitator Koenike of A. geminus George; A. insperatus George of A. stjoerdalensis Thor; Arrenurus brachyurus Viets of A. bifidicodulus Piersig and Arrenurus truncatellus georgei Piersig of A. truncatellus (Müller). A. spatiosus Viets has been raised to species rank, while A. papillator bicolor Viets should stand as a subspecies. A. distans Walter, A. scourfieldi Soar and A. tubulator (Müller) are considered good species. A. bueranus Münchberg, A. curtus George, A. incertus Biesiadka, A. soari George and A. paluster Thor are considered species incertae. A lectotype has been designated for A. scourfieldi. Finally, a small number of old identifications have been re-examined.

Aspects of the egg biology of the perlid stonefly, Dinocras cephalotes (Curtis), were studied experimentally. Development under constant laboratory conditions did not differ from development under variable field conditions. Exposure to 4°C, the lower threshold temperature for egg development, caused abrupt interruptions of embryonic development. Development was resumed after return to favourable temperatures, with an approximate two-week-delay. Up to six interruptions of egg development did not negatively affect hatching success, regardless of developmental stage at which disturbances occurred. However, the older embryos grew, the more rapidly development was resumed after a cold disturbance; embryos from fully developed eggs hatched even at 4°C, although this is too cold to support larval growth. While eggs at 4°C remain dormant and vital for long periods of time, eggs exposed to suboptimal temperatures (10°C) remain only temporarily dormant and eventually develop and hatch.D. cephalotes is assumed to satisfy its high thermal demand for egg development under harsh conditions, for example in arctic Scandinavia, by opportunistically using summer warmth and spreading embryogenesis over more than one year. I suggest that high cue temperatures required to initiate egg development in Scandinavian populations are adaptive and ensure that larvae in the Arctic hatch under favourable seasonal conditions.

The genus Paracloeodes (Insecta : Ephemeroptera : Baetidae) is newly reported from South America. Because of the discovery of species with hindwings and other characteristics not previously associated with Paracloeodes, a redescription of the genus is provided. Cladistic data suggest a South American center of origin for this Panamerican genus. Paracloeodes binodulus,n. sp., is described from larvae from northern Brazil, and is distinguished by the lack of hindwingpads and presence of small mesonotal tubercles. Paracloeodes eurybranchus n. sp., is described from larvae and female adults from north-central Argentina and southeastern Brazil; it is distinguished as larvae by the relatively large size, hindwingpads, and medially broad gills. Paracloeodes ibicui, n. sp., is described from a mature larva collected from Paraguay, and is distinguished by hindwingpads andabdominal coloration. Paracloeodes leptobranchus, n. sp., is described from larvae from Paraguay and southeastern Brazil, and is distinguished by relatively large size, hindwingpads, and slender gills.

During the summers 1992 and 1993, 15 species of Clinocerinae (Empididae) were collected on Corsica. The illustrated descriptions of six new species are given: Roederiodes wagneri sp. n., Clinocera (Kowarzia) cataractae sp. n., Wiedemannia (Chamaedipsia) ariolae sp. n., Wiedemannia (Chamaedipsia) bravonae sp. n., Wiedemannia (Philolutra) kallistes sp. n. andWiedemannia (Wiedemannia) martini sp. n.. Their systematic relations with other species are discussed. Informations is given about their geographic distribution and their habitats.

L'utilisation des microhabitats par le vairon, Phoxinus phoxinus (L.), le goujon, Gobio gobio (L.) et la loche franche, Barbatula barbatula (L.) a été étudiée en conditions d'étiage d'hiver et d'été dans trois rivières du sud-ouest de la France : l'Ariège, la Nive et le Gave de Pau. Les poissons ont été échantillonnés par pêche électrique selon la méthode de l'Echantillonnage Ponctuel d'Abondance. Onze variables du milieu ont été prises en compte pour décrire l'environnement ponctuel des poissons. Pour chaque rivière, les associations interspécifiques et espèces-variables du milieu ont été calculées et comparées en fonction de la saison.Des variations saisonnières de l'utilisation du microhabitat et des associations interspécifiques ont été observées sur les trois rivières. La nature du substrat et la présence d'abris végétaux jouent un rôle important dans la microrépartition du vairon, du goujon et de la loche franche. Ces structures offrent aux poissons des habitats de refuge et de nutrition privilégiés.

A study has been carried out on the acid soluble fraction (hydrosysis at pH 1.5, 3N HCl, 20 % KCl) of organic matter (OM) in the highly calcareous lacustrine sediments of the Jura region, France. Amino acids (AA's) were quantified and determined ninhydrin photometry and HPLC respectively. There was a high degree of interference by calcium in both procedures. The mechanism of interference is explained and methodology adopted to overcome it, by removal of calcium, are dealt with. The results of both methods are compared.