CERITHIID^E. 115 



Genus FASTIGIELLA, Reeve, 1848. 



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

 spiral riblets ; aperture terminating 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 whorls 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 with lanceolate foot, subtruncate in front ; eyes placed at 

 the external base of the rather long tentacles ; operculigerous lobe 

 with rudimentary expansions on the sides , siphon rudimentary. 



Numerous small species inhabiting temperate waters. 



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

 synonyms. 



Section CERITHIDIUM, Monts., 1884. 



Mouth somewhat rounded, scarcely showing any canal below. 



C. SUBMAMILLATUM, Rayil. 



Genus POTAMIDES, Brongniart, 1810. 



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

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

 whorls numerous, narrow, the last short ; aperture channeled in 

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

 spiral. 



Animal with 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 with 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 

 with a large external wing (PL 19, fig. 2). 



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



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

 cularly swamps, and the mouths of rivers, where they frequently 

 remain for long periods out of the w r ater, and in the dry season 



