BY E. M. JOHNSTON, F.L.S. 



87 



G-enus Cbeithium. Brug. (248-259.) 

 Shell turreted, many whorled, with indistinct varices ; 

 aperture small, with a tortuous canal in front ; 

 outer lip expanded ; inner lip thickened ; operculum 

 horny, spiral. Dist. — Almost world-wide. 



Sub-Genus Bittium. 

 Shell elevated, with numerous granular whorls and irregular 

 varices ; anterior canal short, not recurved; inner lip 

 simple ; outer lip not reflected ; usually with an exterior 

 rib ; operculum four whorled. 



Genus Tkiforis. Deshayes. (260-261.) 

 Shell sinistral, sculptured, granular ; whorls numerous, 

 terminating below in a small aperture with tubular 

 anterior canal ; opposite this canal is sometimes a 

 second one upon a varix, marking the position of a 

 former aperture ; operculum orbicular, few- whorled. 

 Dist. — East Indies, Polynesia, Panama, West Indies, 

 Mediterranean, Australasia. 



Genus Potamidbs. Brong. (262.) 

 Shell often large sized, turriculated ; whorls angulated and 

 coronated ; aperture prolonged in front into a nearly 

 straight canal ; outer lip thin, sinuous ; epidermis thick, 

 olive brown ; operculum many whorled. Dist. — 

 Tropical and sub-tropical ; fresh and brackish streams 

 and swamps. 



(xxxv.) Family Rissoellid^i. 

 Genus Tatea. Tenison- Woods. (263.) 

 Shell minute, elongate, pyramidal, attenuate, with brownish- 

 black epidermis; spire elevated, acuminate; whorls 

 flattish (8) ; aperture pyriform ; inner lip reflected ; 

 operculum horny and thin, with a vertical sub-marginal 

 claw. Dist. — Only one representative, T. Huonensis, 

 T. Woods. Pound under stones at low water in tidal 

 estuaries in Tasmania. 



(xxxvi.) Family Rissoidjs. 



Shell small, spiral, turreted or depressed, often more or less 

 umbilicated ; aperture more or less rounded, never 

 truly channeled in front ; peritreme continuous. 



Sub-Family Rissoinime. 

 Shell small, ovate, or turreted with a thick corneous or 

 calcareous pauci-spiral operculum, with internal process, 

 articulated (marine). 



