CERITHIID^. 115 



Genus FASTIGIELLA, Reeve, 1848. 



Perforate, elongated, turreted ; Avliorls numerous, convex, with 

 spiral riblets ; aperture ternnnating in a short, slightly twisted 

 canal. 



One or two recent species occur in the West Indies, and several 

 fossils from the Eocene of the Paris basin are also referred here. 



Genus BITTIUM (Leach\ Gray, 1847. 



Shell elevated, with numerous granular Avhorls and irregular 

 varices ; anterior canal short, not recurved ; inner lip simple, outer 

 lip not reflected, usually with an exterior rib. Operculum four- 

 whorled with central nucleus. 



Animal Avith lanceolate foot, subtruncate in front ; eyes placed at 

 the external base of the rather long tentacles ; operculigerous lobe 

 Avith rudimentaiy expansions on the sides , siphon rudimentary. 



Numerous small species inhabiting temperate Avaters. 



Cerithiolum, Tiberi, 1869, and Platygyra, Morch, 1860, are 

 synonyms. 



Section Cerithidium, Monts., 1884. 



Mouth somcAvhat rounded, scarcely shoAA'ing any canal beloAV. 

 C. SUBMAMILLATUM, Rayn. 



Genus POTAMIDES, Brongniart, 1810. 



Imperforate, turreted, angulated, tuberculate, spiny, etc., and 

 covered by a thick, olive-brown epidermis, apex often decollated ; 

 Avhorls numerous, narroAV, the last short ; aperture chaimeled in 

 front, outer lip simple or thickened. Operculum corneous, multi- 

 spiral. 



Animal Avith subcircular foot, obtuse behind ; eyes on the 

 side of the tentacles at a third or half of their length ; siphon usually 

 fringed. 



Middle tooth of the radula small Avith toothed margin, lateral 

 tooth large, subrhomboidal, with a rostrated base and toothed mar- 

 gin, first marginal tooth narrow, with a slight posterior projection, 

 second marginal tooth sometimes elongated and simple, sometimes 

 Avith a large external Aving (PI. 19, fig. 2). 



The type is a fossil, P. Lamarcki, Brongniart. 



Inhabits brackish and fresh AAaters, in Tropical countries, parti- 

 cularly sAAamps, and the mouths of riA^ers, Avhere they frequently 

 remain for long periods out of the AA'ater, and in the dry season 



