MANUAL OF THE MOLLTJSCA. 



Triphoris, Deshayes. C. perversum, PI. VIII., fig. 18. 30 sp. Norway 

 Australia. Fossil. Eocene . Brit., France. Shell sinistral; anterior 

 and posterior canals tubular. The third canal is only accidentally present, 

 forming part of a varix. 



Cerithiopsis, Forbes. C. tuberculare, Brit. Shell like bittium ; proboscis 

 retractile j operculum pointed, nucleus apical. Range 4 40 fms. 



POTAMIDES, Brongniart. Fresh-water Cerites. 

 Etym., potamos, a river, and eidos, species. 

 Type., P. Lamarckii, Brong. (=*= Cerit. tuberculatum, Brard.) 

 Ex., P. mixtus. PI. VIII., fig. 19. 



Syn., 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 ; epidermis thick, olive- 

 brown ; operculum orbicular, many-whirled. 



Distr., old world only ? Africa, India. In the mud 

 of the Indus they are mixed with sp. of ampullaria, 

 veiius, purpura, vulsella, &c. (Major W. E. Baker.) 



Fossil (sp. included with cerithium) Eocene . 

 Europe. 



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. 78. 



Distr. 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 whirls 

 (as in nerinaa, fig. 79). India, N. 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, Montf. Cerit, palustre, PL VIII., fig. 20. 

 Shell with numerous indistinct varices ; canal straight, often tubular ; 

 outer lip expanded. India, N. Australia. 



Cerith radulum and granulatum of the W. African rivers approach very 

 nearly the fossil pot amides, but they have numerous varices. 



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



