. Bulletin of the Natural History Museum Zoology. 132 TAYLOR, KANTOR AND SYSOEV tip (Fig. 12). This sac is covered in granule-like structures which are formed from single cells with large rounded nuclei. The distinctive epithelial cells seen at the proboscis tip of Mangelia nebula by Sheridan et al. (1973) may be the same structure but in a more contracted position. The function of this sac structure is not known. Position of the buccal mass Three conditions are known in the Conoidea; a) Buccal mass situated at the base of the proboscis (Fig. 1) For three reasons we consider thi
. Bulletin of the Natural History Museum Zoology. 132 TAYLOR, KANTOR AND SYSOEV tip (Fig. 12). This sac is covered in granule-like structures which are formed from single cells with large rounded nuclei. The distinctive epithelial cells seen at the proboscis tip of Mangelia nebula by Sheridan et al. (1973) may be the same structure but in a more contracted position. The function of this sac structure is not known. Position of the buccal mass Three conditions are known in the Conoidea; a) Buccal mass situated at the base of the proboscis (Fig. 1) For three reasons we consider this condition to be the primitive state within the Conoidea. Firstly, a basal buccal mass is found in species of the subfamily Drilliinae, which with five teeth in each radula row, are considered to possess the least-derived type of radula. Secondly, and also in the Drilliinae, there is a muscular connection between the retrac- tor muscle of the radular sac and the columellar muscle (Kantor, 1990). This is a condition found in some meso- and archaeogastropods, as for example in Littorina, Cryptonatica and Tegula (Fretter & Graham, 1963; Kantor, unpublished observations). In most other probosciform gastropods, including those turrids where the buccal mass lies within the proboscis, this connection is broken and the radula is con- nected by muscles to the walls of the proboscis. Finally, the basal buccal mass is a character-state shared amongst most of the subfamilies of Turridae, along with the Terebridae, Pervicaciidae and Conidae. b) Buccal mass located within the proboscis In Clavatula diadema (Clavatulinae), the buccal mass lies within the proboscis, but in a proximal position (Kantor, 1990, fig. 8). In Clionella sinuata (Clavatulinae), Pilsbryspira nympha (Zonulispirinae) and Funa latisinuata (Crassispiri- nae), it lies more anteriorly, about half way along the proboscis (Figs 6 & 14). In Strictispira paxillus (Strictispiri- nae) (Fig. 13), Toxiclionella tumida (Clava
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