99 Mr Gray on Testaceous Mollusca, 



The greater number of species of the genus Cerithium are 

 truly marine, chiefly living in sandy bays, like our own Ceru 

 thium reticulatuvi. M. Lesson, however, found C, sulcatum^ 

 and Adanson the African species figured by him, in the pools of 

 brackish water, sometimes overflov/ed by the sea, which are si- 

 tuated between the weeds and the belts of mangrove trees on the 

 shore ; and Mr Say observes that the small species called by 

 him Pyrena scalar ifor mis ^ but which is a true Cerithium^ is 

 found in great abundance in the fresh water of Florida Keys. 

 He adds, " It is most certainly a fresh water shell, yet it is desti- 

 tute of an epidermis." 



V The genus Bulla is also truly marine ; but the Rev. Mr 

 Hennah some time since presented to the British Museum spe- 

 cimens of one of its species, resembling the Bulla Hydatis^ found 

 by him in brackish pools on the coast of Chili ; and Mr Say has 

 described a Bulla Jluviatilis found by Mr Aaron Stone deeply 

 imbedded in the mud of the river Delaware.* 



The Littorince^ again, are all found either on the sea-shore or 

 in the very brackish waters of the mouths of rivers, except two, 

 which, although described as PaludincB by PfeifFer and De 

 F^russac, and formed into a distinct genus by Ziegler under 

 the name of Lithoglyphus^ agree with Littorina in every cha- 

 racter of shell and operculum, and, as far as I can ascertain 

 from the descriptions, of the animal also. These are the Palu* 

 dina Jusca of PfeifFer, and the P. naticoides of De Ferussac ; 

 they are truly fluviatile. 



These anomalies are not restricted to the univalves : bivalves 

 have also their share. Thus, the genus Solen is generally and 

 properly considered as marine ; but Mr Benson has lately disco- 

 vered a species inhabiting the mud on the banks of the Ganges ; 

 and conceiving, from the nature of its habitation, that it ought 

 to be separated from the common species, he has formed a ge- 

 nus for its reception, under the name of Novaculina. On com- 

 paring, however, some specimens of the shell presented to the 

 British Museum by Mr Royle, lean scarcely distinguish it as a 

 gpecies from the Solen Dombeyi of Lamarck, which is found on 

 the coast of Peru ; and I have two other species, very nearly re- 



• See for this latter instance the Journal of the Academy of Natural 

 Sciences of Philadelphia, vol. ii. p. 179. 



