16 BULLETIN 68, UNITED STATES NATIONAL MUSEUM. 



A' Postnuclear whorls sculptured similarly throughout — Continued. 

 B' Varices absent — Continued. 



C^ Axial sculpture absent, shell polished — Continued. 

 Summits of the whorls not tabulated. 

 Columellar fold present. 



Peritreme discontinuous, aperture not rissoid. 

 Shell inflated, very large. 

 Subgenus Amaura Moller, 1842 (p. 218). 

 Type, Amaura Candida Moller. 



Shell not inflated. 



Subgenus Odostomia Fleming, 1817 (p. 231). 



Shell of medium size. 

 Section Odostomia Fleming, s. s. (p. 231). 



Type, Turbo plicatus Montagu. 



Shell rather large. 

 Section Stomega Dall and Bartsch, 1904 (38). 

 Type, Odostomia conspicua Alder. 



Shell small. 

 Section Brachystomia Monterosato, 1884 (39). 

 Type, Odostomia rissoidea Hanley. 



Peritreme continuous, aperture rissoid. 



Subgenus Heida Dall and Bartsch, 1904 (p. 231). 

 Type, Syrnola caloosaensis Dall. 



Columellar fold obsolete. 

 Shell umbilicated. 



Subgenus Myxa Hedley, 1903 (40). 

 Type, Myxa exesa Hedley. 



Shell not umbilicated. 



Peritreme continuous, aperture rissoid. 

 Subgenus Pseudorissoina Tate and May, 1900 (41). 

 Type, Stili/er tasmanica Tenison-Woods. 



Peritreme not continuous, aperture not rissoid. 

 Subgenus Liostomia O. Sars., 1878 (42). 

 Type, Risscella? eburnea Stimpson. 

 B 2 Varices present. 



Shell smooth, axial sculpture indicated by a few varices, spiral sculpture 

 wanting. 



Subgenus Oceanida De Folin, 1870 (43). 

 Type, Oceanida gradata De Folin. 



Shell with sublamellar axial ribs. 

 Salassiella new subgenus (p. 133). 



Type, Odostomia (Salassiella) laxa new species. 



A- Early postnuclear whorls sculptured differently from the later ones. 



Early postnuclear whorls loosely coiled, plain; later ones closely coiled with a 

 spiral keel at the periphery and one at the summit of the whorls; base spirally 

 Urate. 



Subgenus Lysacme Dall and Bartsch (p. 132). 

 Type, Chrysallida clausiliformis Carpenter. 



Early postnuclear whorls axially ribbed, succeeded by one or two strongly spirally 

 and faintly axially Urate whorls; the rest of the whorls are marked by a reticu- 

 lated sculpture consisting of raised axial and spiral cords. 

 Subgenus Obtortio Hedley, 1899 (44). 



Type, Rissoa pyrrhacme Melvill and Standen, 1899. 



