BRYOZOAN FRONTAL SHIELDS - THE TYPE SPECIES OF DESMACYSTIS, RHAMPHOSTOMELLA, RHAMPHOSMITTINA, RHAMPHOSTOMELLINA, AND NEW GENUS ARCTONULA

Frontal shields have been examined in the type species of several gene ra of ascophorine cheilostomates. Desmacystis (Desmacystidae) is not a n 'anascan' as previously thought, but has a cryptocystal shield which is here interpreted to be derived from an umbonuloid shield by foresh ortening, possibly from a rhamphostomellan ancestor. Rhamphostomella ( type species R. scabra) and Rhamphosmittina (type species R. bassleri) (both in the family Porellidae Vigneaux, here raised from subfamily r ank) also have umbonuloid shields. Arctonula, new genus, is establishe d for Lepralia arctica M. Sars and transferred from the Umbonulidae to the Exochellidae. Rhamphostomellina (type species R. posidoniae) has a lepralioid shield. It is here included in the family Celleporidae.