GASTEROPODA. 



243 



Sliell like Intthnn ; proboscis retractile; operculum pointed, 

 nucleus apical. Exinge 4 — 40 fathoms. 



POTAMIDES, Brongniart. Fresh- water Cerites. 



Etymology, 2^otamos, a riyer, and ides, patronj^mic termination. 



Type, P. Lamarckii, Brong. (= Cerit. tuberculatum, 

 Brard.) 



Example, P. mixtus. PI. VIII., Fig. 19. 



Synonyms, TjTnpanotomu^, Klein, 0. fuscatum, Africa. 

 Pirenella, Eisso, 0. mammillatum, PI. YIIL, 

 Fig. 22. 



Shell like ceritlnum, but without varices in 

 the very numerous typical fossil species ; epi- 

 dermis thick, oliye brown; operculum orbicular, 

 many-whorled. 



Distribution, 41 species. California, Africa, 

 India. In the mud of the Indus they are 

 mixed with species of ampuUaria, venus, 

 imrpura, ostrea, &c. (Major W. E. Baker.) 



Fossil (species included with cerithium), 

 Eocene — . Europe. 



Sub-genera, Cerithiclea, Sw., C. decoUata, 

 PI. YIIL, Fig. 24. Aperture rounded; lip 

 expanded, flattened. Inhabit salt marshes, 

 mangrove swamps, and the mouths of rivers ; 

 they are so commonly out of the water as to have been taken for 

 land-shells. Mr. Adams noticed them in the fresh waters of 

 the interior of Borneo, creeping on pontederia and sedges ; they 

 often suspend themselves by glutinous threads (Fig. 97). 



Distribution, India, Ceylon, Singapore, Borneo, Philippines, 

 Port Essington. 



Terebralia, Sw. Cerith. telescopium, PI. YIIL, Fig. 21. 



Shell pyi-amidal; columella with a prominent fold, more or 

 less continuous towards the apex; and a second, less distinct, on 

 the basal front of the whorls (as in nerincea (Fig. 98). India, 

 North Australia. 



T. telescopium is so abundant near Calcutta as to be used for 

 burning into lime ; great heaps of it are first exposed to the sun, 

 to kill the animals. They have been brought alive to England. 

 (Benson.) 



Pyrazus, Montfort. Cerit. palustre, PI. YIIL, Fig. 20. 



Shell with numerous indistinct varices ; canal straight, often 

 tubular ; outer lip expanded. India, North Australia. 

 * C. obtusa, Lam. sp. copied from Adams. 



m2 



Tm. 97. Cerithidea.* 



