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. 



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

 synonyms. 



Section CERITHIDIUM, Monts., 1884. 



. Mouth somewhat rounded, scarcely showing any canal below. 

 C. SUBMAMILLATUM, Rayn. 



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 w r ith 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 (PI. 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 water, and in the dry season 



