Habite dans la Garonne et les rivières qui s'y jettent.
MATERIALS AND METHODSThe snails were collected from four places in the Garonne basin: Saint Léger (on Garonne river), Viale (on Baïse river), Clairac (on Lot river), tank at Saint Étienne de Fougères. Additional samples were collected from an artificial pond at Montpellier and a canal at Perpignan.The specimens to be dissected were relaxed for 8 h in a 0.05% solution of nembutal. Then they were immersed for 40 sec in water heated at 70 o C, from which they were transferred to water at room temperature. The animals (under water) were drawn from the shell with a small forceps applied to the cephalopedal mass, and fixed in slightly modified Railliet-Henry's fluid (distilled water 930 ml, sodium chloride 6 g, formalin 50 ml, glacial acetic acid 20 ml).Voucher specimens were deposited in the Museum National d'Histoire Naturelle (Fig. 1) elongate-ovate, thin, smooth, moderately lustrous and translucent, light fawn colored; fine, closeset lines of growth, non-perceptible spiral lines. Protoconch distinct, rounded exserted. Whorls 5, regularly and rapidly increasing, the first minute, the last very large, roundly shouldered. Spire short. Suture slightly impressed. Aperture large, ear-shaped, about ¾ total length of shell; outer lip thin, sharp; inner lip closely appressed to the columellar region completely closing the umbilical region; columellar plait somewhat twisted; parietal callus wide, columellar fold well marked. Largest shell 16 mm in length, 9 mm in width.Cephalopedal mass uniformly dark gray. Fig. 2 shows some features of a crawling specimen: labial palps fanlike, slightly bilobed anteriorly, roundly angled laterally; foot tapering to a pointed caudal tip that does not overreach the shell apex. Roof of pulmonary cavity deeply pigmented and flecked with small circular to oval unpigmented spots. Renal tube (Fig. 3, rt), as usual in physids, tightly folded into a zig-zag course, ending by a short ureter which opens through a subterminal meatus just behind the pneumostome. Mantle collar (Fig. 3, mc) with about 3-5 digitations on the apical (ad) and 5-10 on the columellar (cd) region, reflected -the latter more extendedly -over the edge of the shell. By the way, in the original description of P. acuta it is stated that "the animal has no mantle digitations at all", whereas seven digitations over the columella are mentioned by Moquin-Tandon (1855).Reproductive system (Fig. 4) -Ovotestis (ot) embedded in the digestive gland. Ovotestis follicles (about 80 in a minutely dissected specimen) emptying into a collecting canal which continues into the ovispermiduct. Between the proximal (od 1 ) and distal (od 2 ) segments of the latter are the seminal vesicles (sv). The ovispermiduct empties into the carrefour, as well as the albumen gland (removed in the figured specimen).From the carrefour the oviduct (ov) emerges as a narrow tube which runs leftwards, gradually widens, becomes