550 



MOLLUSCA 



PHYLUM VI 



transverse ribs and spiral Striae. Aperture contracted, rounded, without canal, some- 

 times slightly separated off, and with continuous peristome. Abundant in the Jura. 

 Bittium Leacli (Fig. 980). Turreted, with granulated spiral ribs, 

 and numerous transverse costae. Aperture with short, straight canal ; 

 outer lip sharp. Jura to Kecent. Abundant in the Tertiary. 

 Triforis Deshayes ; Gerithiopsis Forbes. Tertiary and Recent. 



Eustoma Piette. Aperture with 

 long canal, which is often closed, 

 however, by margins of the inner 

 and outer lip. Inner lip callous 

 and strongly dilated ; outer lip 

 expanded. Jura. 



Gerithium Brug. (Figs. 981, 

 982). Turreted, imperforate, with- 

 out epidermis. Aperture oblong, 

 ovate, with backwardly curved 

 canal ; outer lip often soinewhat 

 reflected. Columella concave, fre- 

 quently with one or two folds. 

 Certain Tertiary species attain a length of half a metre (C. giganteum). Jura to 

 Recent ; maxinium in Eocene. 



Subgenera : Vicarya d'Arch. ; Glava Martyn (Fig. 982) ; Bellardia Mayer, etc. 



Potamides Brongt. (Figs. 983, 984). Turreted, with epidermis; aperture with 

 emargination or faint canal. Inhabits only brackish water or 

 estuaries. Cretaceous to Recent. 



Fig. 978. 



Fibula undulosa 

 Piette. Bathon- 

 ian ; Bparcy, 

 Aisne. 



Fig. 979. 



Exelissa strangu- 

 lata (d'Arch.). 

 Bathonian ; 

 Eparcy, Aisne. 



Fig. 980. 



Bittium plicatum 

 Brug. Oligocene; 

 Ormoy, near Etampes, 

 France, 



Fig. 981. 



Gerithium serratum 

 Brug. Calcaire Gros- 

 sier ; Damery, near 

 Epernay. 



Fig. 982. 



Cerithium {Glava) 

 nudum Lam. Eocene ; 

 Chaumont, near Paris. 



Potamides (Tympano- 

 tomus) margaritaceum 

 Brocchi. Oligocene ; 



Hackenheim, near Alzey. 



Subgenera : Tympanotomus Adaras (Fig. 983) ; Pyrazus, Telescapium Montf. 

 Swains. ; Lampania (Fig. 984) and Pyrenella Gray ; Sandbergeria Bosq. 



Fig. 984. 

 Potamides (Lampania) 

 pleurotomides Desh. 

 Middle Meeressand ; 

 Mortetbntaine, 8eine-et- 

 Oise. 



Cerühidea 



Family 18. Aporrhaidae Philippi. 



Shell fusiform, turreted or conical ovate. Aperture produced anteriorly in a canal. 

 Outer lip expanded in a wing-like or digitiform fashion^ or thickened. Operculum horny. 

 Marine. Jura to Recent ; maximum in Jura and Cretaceous. 



Älaria Morris and Lyc. (Figs. 985-988). Shell turreted ; aperture with long or 

 Short canal. Outer lip not overriding the last whorl, digitated or winged. Spire 



