The Limousin ophiolite (French Massif Central) occurs as elongate bodies forming a (nearly) continuous suture zone between two major lithotectonic units of the French Variscan belt. The mantle section of the ophiolite is made of diopside-bearing harzburgite, harzburgite and dunite characteristic of a lherzolite-harzburgite ophiolite type (LHOT). The plutonic section is essentially composed of troctolites, wehrlites and gabbros locally intruded by ilmenite-rich mafic dykes. All the rocks were strongly affected by an ocean-floor hydrothermal metamorphism. The composition and evolution of primary magmatic phases (olivine, clinopyroxene, plagioclase and spinel) throughout the lowermost magmatic sequence correspond to those described in oceanic cumulates (ODP data). The Limousin ophiolite is thus of MOR type instead of SSZ type. The whole lithological section, the mineral chemistry, the extensive hydrothermal oceanic alteration and the relatively thin crustal section are typical of a slow-spreading ridge ocean (i.e. Mid-Atlantic ridge). Comparison of the Limousin ophiolite with other ophiolites from European Variscides suggests that the oceanic domain was actively spreading during the Late Palaeozoic and extended from the Armorican massif to the Polish Sudetes.

Field investigations in two lymnaeid habitats located along river banks were carried out over three years to study snailcolonization in relation to water-level variations, to determine the number of annual generations, and to analyse the ability ofG. truncatula to emerge from water. As these river banks were located 6.7 km upstream from a dam, water recedes each day,thus permitting the study of snails on banks for several hours per day. From March to December, snails followed seasonal variationsof water-level. However, only a few G. truncatula were observed following the daily retreat of water. Two annual generationsof G. truncatula, the first from the onset of July and the second in December, were noted in these habitats. When waterreceded each day, the mean distance covered by non-aestivating snails ranged from 25 to 44 cm. However, they escaped waterrise by seeking refuge in still emerged zones of their habitats. From July to October, snails following each day water recedingshowed a significantly quicker growth than that of G. truncatula which only moved in the same zone of their habitat. Populationsof G. truncatula living along these river banks would be completely adapted to their habitat. The escape of snails from waterrise between July and October might correspond to a physiological reaction of survival when a too rapid increase of water-leveloccurs.

Des investigations malacologiques ont été réalisées en 1974 et en 1994-1995 dans trois prairies de la Haute-Vienne afin depréciser les caractéristiques des gîtes à limnées lorsque les parcelles sont abandonnées ou modifiées par l'application de mesures agronomiques. L'abandon d'une prairie et l'invasion de ragondins se sont traduits par des modifications dans la distribution des limnées. Lymnaea cf. fuscus a déserté le fossé principal de drainage pour coloniser les rigoles et les couloirs créés par ces rongeurs,ce qui s'est traduit par un accroissement important de la superficie du nouveau gîte. Les effectifs moyens de L. cf. fuscus et de L. truncatula ont augmenté aux dépens de ceux de L. glabra. Un autre mollusque aquatique, Physa acuta, a envahi le fossé laissé libre. Le curage des rigoles dans les deux autres prairies et leur invasion par une ou deux espèces aquatiques (L. ovata, Potamopyrgus antipodarum ou Physa acuta) se sont traduits par une extension dans la superficie du gîte aussi bien pour les mollusques colonisateurs que pour L. glabra et L. truncatula. Les effectifs des trois premières espèces sont assez importants dans ces deux rigoles ; par contre, on note une réduction du nombre des deux limnées.