GASTEEOPODA. 243 



Shell like hittium ; proboscis retractile ; operculum pointed, 

 nucleus apical. Eange 4 — 40 fathoms. 



PoTAMiDES, Brongniart. Fresh- water Cerites. 



Etymology, potamos, a river, and ides, i)atronyniic termination. 



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

 Brard.) 



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



Synonyms, Tjnnpanotomus, Klein, C. fuscatum, Africa. 

 Pirenella, Eisso, 0. mammillatum, PL YIII., 

 Fig. 22. 



Shell like cerithium, but without varices in 

 the very numerous typical fossil species ; epi- 

 dermis thick, olive 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, 

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



Fossil (species included with cerithium), 

 Eocene — . Europe. 



Suh-genera, Cerithidea, Sw., C. decollata, 



Pi. YIII., Fig. 24. Aperture rounded; lip 



expanded, flattened. Inhabit salt marshes, 



^ , , , A-L n • Fig- 97. Cerithidea,* 



mangrove swamps, and the mouths oi 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). 



Distrihution, India, Ceylon, Singapore, Borneo, Philippines, 

 Port Essington. 



Terehralia, Sw. Cerith. telescopium, PI. YIII., Fig. 21. 



Shell pyramidal; 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 

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

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

 (Benson.) 



Fyrazus, Montfort. Cerit. palustre, PI. YIII., Fig. 20. 



Shell with numerous indistinct varices ; canal straight, often 

 tubular ; outer lip expanded. India, North Australia. 



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

 M 2 



