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

boring origin. The canals belong to an oriented ramification system which is definitely indicative of an organism living in colonies. The initial part of the canal system is at the parietal lip of the gastropod (Text-fig. 1). From this area the colony developed following the growth of the shell. Branchings are bifurcate in every Text-fig. 1 - Drawing of the basal traces of a colony on Proconulus baldensis (specimen J 10 144) with visible primary canal (PC). Arrows indicate two kinds of false crossing of excavations (see also "Description"); x 14. case with an average angle of 45° (Pl. I, Fig 1.). In general, the angle of the posterior branch and the growth line crossing the point of bifurcation is smaller than that at the anterior one (Pl. II, Fig. 1). However, following a short, relatively wide and curved part, the other branch forms the same angle to the growth lines but anteriorly. On the stratigraphically youngest gastropod the angle of bifurcations is about 60°; the posterior canal is much nearer to the growth line crossing the area of bifurcation than the anterior one which may be almost parallel to the spiral ornament of the gastropod. On the stratigraphically older specimens, grooves, nearly parallel to the growth lines, occur only along the inner lip. That is the area where the canals are most closely spaced (Pl. II, Fig. 2). The excavations never cross each other but a few false cases may occur when a canal terminates near a bifurcation (Text-fig. 1: outlined arrow). Sometimes two points of oppositely directed branchings are close to each other also resulting in an apparent crossing (Text-fig. 1: black arrow). Orientation on gastropod shell - Abaperturally, all the colonies are bounded by a definite canal (= "primary canal") which runs from the parietal lip to the pe-