IIYDROCENA. 299 



cinerascens, Eossm. Porroi, Strobel. 



gracilis, Kust. scalarinus, Villa. 



maculatus, Brap. striolatus, Porro. 



obscurus, Brap. tessellatus, Wieym. 

 patulus, Brap. 



Genus IIYDROCENA, Parreyss. 



Operculum thin, homy, pauci-spiral. 



Shell imperforate or umbilicated, turreted or glohosely 

 turbinate, simple, or keeled around the perforation ; aperture 

 oval; peristome with the margins disjoined, straight or ex- 

 panded. 



Ex. H. rubens, Quoy and Gaimard, pi. 87, fig. 2. 

 Operculum, H. rubens, fig. 2, a, 2, b. Shell, H. rubens, 

 fig. 2, c. 



The Pacific Islands, Opara, Tahiti, Tonga, and the Fijis, 

 are the principal countries inhabited by the species of this 

 genus. 



Species of Hydroceita. 



albescens, Pfeiff. minutissiraa, Sow. 



brevicula, Pfeiff. multilineata, Pfeiff. 



Bridgesi, Pfeiff. oblonga, Pfeiff. 



Cattaroensis, Pfeiff. obtusa, Pfeiff. 



cornea, Pfeiff. pyramis, Pfeiff. 



exserta, Pfeiff. solidula, Pfeiff. 

 gutta, Shuttl. 



Sub-gen, realia, Gray (Liarea, Gray). 



Shell turreted, thin, rather smooth ; aperture ovate ; peri- 

 stome continuous, double. 



Egea, Gray. turriculata, Pfeiff. 



rubella, Pfeiff. ventricosa, Hombr. and Jacq. 



