GASTEROPODA. 943 
Shell like bittium ; proboscis retractile; operculum pointed, 
nucleus apical. Range 4—40 fathoms. 
PoTAMIDES, Brongniart. Fresh-water Cerites. 
Etymology, potamos, a river, and ides, patronymic termination. 
Type, P. Lamarckii, Brong. (= Cerit. tuberculatum, 
Brard.) 
Example, P. mixtus. Pl. VIII., Fig. 19. 
Synonyms, Tympanotomus, Klein, C. fuscatum, Africa. 
Pirenella, Risso, C. mammillatum, Pl. VIII., 
Fig. 22. 
Shell like cerithium, but without varices in 
the very numerous typical fossil species; epi- fi NOS 
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 ampullaria, venus, 
purpura, ostrea, &c. (Major W. H. Baker.) 
Fossil (species included with cerithiwm), 
Kocene—. LHurope. 
Sub-genera, Cerithidea, Sw., C. decollata, 
Pl. VIII, 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, Pl. VIII., 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 
barning 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, Pl. VIII., Fig. 20. 
Shell with numerous indistinct varices; canal straight, often 
tubular; outer lip expanded. India, North Australia. 
* C. obtusa, Lam. sp. aa from Adams. 
NM 
Fig. 97. Cerithidea,* 
