Vörös A. szerk.: Fragmenta Mineralogica Et Palaentologica 15. 1992. (Budapest, 1992)

riphery and further to the suture without any posterior branch (Text-fig. 1; Pl. Ill, Fig. 1). Between the periphery and the suture, it is much more prosocline than the growth lines but their angle is nearly constant, so the primary canal is also feebly prosocyrt. On some shells more than one primary grooves appear at different growth stages of the gastropod. However, it is not possible to decide whether they have belonged to independent colonies or only to different generations of a single one, since the basal areas of the spire whorls are covered. None of the excavations crosses the suture. INTERPRETATION OF THE TRACES The basal area of the excavation network is frequently overgrown by subsequent whorls of the gastropod. This phenomenon proves the contemporaneous life of Proconulus baldensis specimens and the epibiont but the ecological category of the coexistence needs some speculation. First, it is necessary to decide whether the traces are of animal or plant origin. Compared with reviews by Bromley (1970) and Glaub (1988), the morphology and dimensions of the borings studied here resemble those of some Thallophyta (Cyanophyta, Chlorophyta, Rhodophyta, Mycophyta) and some Invertebrata. However, a photophilous plant origin is not likely because the densest parts of the colonies are usually found on the base of the shells. In life position, this is the darkest region and at the same time, there is no tendency in the development of the colonies toward light (i.e. to the top of the shell). On the contrary, the delimitation of the colonies by the suture (and the "frontier marker" primary canal) is clearly visible. Numerous excavations are oriented back to the lightless inner lip regions (Pl. I, Fig. 2; Pl. II, Fig. 2; Pl. IV, Fig. 2; Text-fig. 1.). Therefore only a fungal borer can be considered from Thallophyta but the canals are much wider (0.04-0.07 mm) than those produced by Mycophyta which are usually less than 0.005 mm, only exceptionally larger (Glaub, 1988). Bromley (1970) pointed out that canals wider than 0.05 mm cannot be regarded as fungal borings. Assumption of a non-thallophytan origin is further supported by the lack of any traces of reproductive organs or characteristic broadenings of the canals which are common in algal and fungal borings. Turning to Animalia, a colony builder origin is suggested by the restriction of the canal system to a near-peristomal position (no branches extending beyond the primary canal and the suture but many of them terminate at or near the peristome). The explanation for this phenomenon may be either a parasitic or a commensalist (or both) mode of life of the epibiont. Commensalism is supported by the fact that the densest part of the excavation network is along the parietal lip where the exhalant current leaves the mantle cavity. However, collection of living or dead tissue particles from the soft body of the gastropod along the peristome/mantle edge is a more likely cause. The traces of the specimen on Pl. IV, Fig. 1-2 support the latter hypothesis. The growth of the gastropod shell halted temporarily three times, first (A and B) to repair fractures then (C), on the last whorl, probably because of the near adult stage or due to some disease of the soft body. In the first two cases, the mantle edge was withdrawn into the shell interior, then a fast shell secretion rendered impossible for the epizoan to follow the growth. Without contact with the soft body of the gastropod (i.e. the food source), the neighbouring individuals died. Certainly, a basal part of the colony survived and it