RIS8OIIDJK. 817 



Section CORENA, A. Adams. 1870. 



Elately turbinate, with obtuse apex, rimate ; aperture circular, 

 peristome duplicate, continuous, outer lip externally reflected, inner 

 lip with thin, callous expansion and posterior tubercle. 



K. TUBERCULIFERA, A. Ad. Gulf of Suez. 



Section AMPHITHALAMUS, Carpenter. 1865. 



Shell smooth, pupoidal, with large nucleus ; peristome duplicated, 

 the inner lip produced forward, with a subbasal space behind it, 

 outer lip joining it posteriorily, suddenly contracted in the adult. 

 California, Australia, Japan. R. INCLUSA, Carp. 



Scrobs, Watson, 1886, is a synonym. 



Section NODULUS, Monts. 1878. 



Shell subcylindrical, with obtuse spire, whorls smooth or feebly 

 spirally striate ; aperture rounded, peristome thick, continuous. 



R. CONTORTA, Jeffreys. 



Peringiella and Pisinna, Monts, 1878, may be united with this 

 group. 



Section ANABATHRON, Frauenfeld. 1867. 



Shell scalariform, with a carinated shoulder, imperforate, smooth ; 

 aperture rounded, peristome continuous. R. CONTABULATA, Frauenf. 



Section PELECYDIUM, Fischer. 1872. 



Imperforate, elongate, sub arcuated, finely striate; whorls some- 

 what flattened, apex mamillate ; last whorl small, descending, de- 

 viating; aperture semicircular, exserted, entire, peristome con- 

 tinuous, somewhat thickened. R. VENUSTULA, Fischer. 



Section HEMISTOMIA, Crosse, 1872. 



Imperforate, elongated, thin, smooth, olivaceous corneous, under 

 a persistent thin epidermis, apex mamillate, obtuse ; aperture a 

 little solute, peristome continuous. 



New Caledonia. R. CALEDONICA, Crosse. 



The characters of this group correspond mainly with those of the 

 preceding one, but the corneous texture and brackish water habitat, 

 have led Dr. Fischer to place it in the Hydrobiidse. If it should 

 prove identical with Pelecydium, the latter name will become a 

 synonym. The operculum of Hemistomia is unknown. 



