250 CERITHIID^. 



numerous, ciugulated ; aperture ending in a twisted, short canal. 

 Operculum very thin, indistinctly spiral, with excentric nucleus. 

 T. granosus, Wood (Ixx, 65). 



PoTAMiDES, Brongniart. 



Etym. — Potamos, a river, and ides, patronymic termination. 

 Fresh-water Cerites. Syn. — Potomis, Swains. 



Distr. — 50 sp. Tropical and subtropical. Fresh and brackish, 

 streams and swamps. Fossil, numerous. Eocene — . P. mamil- 

 latum, Risso (Ixix, 63). P. eheninum, Brug. (Ixx, 66). 



Shell turriculated, whorls angulated and coronated ; aperture 

 prolonged in front into a nearly straight canal ; outer lip thin, 

 sinuous; epidermis thick, olive-brown. Operculum many-whorled. 



BROTiA, H. Adams. Shell fusiform, spire elevated, whorls 

 spinulose, the last subrostrate in front ; aperture subovate, pro- 

 duced anteriorl}'. Operculum corneous, multispiral. Fluviatile. 

 Siam. P. ^ayocZuZa, Gould (Ixx, 67). The type was described 

 as a Melanian, but the operculum at once separates it from that 

 genus. 



TYMPANOTOMUS, Klein. Columella twisted ; outer lip broadly 

 sinuated anteriorly, and less distinctly so posteriorly. P.fuscata, 

 Linn. (Ixx, 68). 



LAMPANiA, (Jray. Shell turriculated, whorls numerous, without 

 varices ; sculpture not prominent ; aperture truncate below ; 

 without canal; outer lip sinuous. P. zonale, Brug. (Ixx, 69). 



PYRAZUS, Montfort. (Terebralia, Swains.) Whorls with 

 revolving striae, not tuberculate ; aperture with a short anterior 

 canal ; columellar callosity spiral, oblique ; outer lip thickened, 

 expanded, rounded anteriorly, and turning upwards to join the 

 inner lip. P. sulcatum,, Brug. (Ixx, 10). P. palustris occurs in 

 great abundance in the salt marshes of the Eastern Archipelago, 

 and is assiduously^ collected by the natives, who roast them and 

 suck the contents of the shell through an aperture made by 

 breaking off the tip of the spire. 



Dr. Brot has made the interesting discovery that the species 

 of this group possess two columellar plicse, and opposite to 

 these, upon the surface of the oviter wall of the shell, are teeth, 

 occurring wherever an external varix has been formed. These 

 do not approach the aperture, and are only discovered upon 

 making a longitudinal section of the shell. They do not occur 

 in the related subgenera, but their presence is mentioned by 

 Deshayes in some of the fossil species of the Paris basin, and 

 they are very characteristic of the fossil genus Neringea, which 

 may thus connect Cerithium and Pyramidella. 



TELESCOPiUM, Montfort. (Terebralia, Swains.) Shell pyram- 

 idal ; columella with a prominent fold, more or less continuous 

 towards the apex ; and a second, less distinct, on the basal front 



