250 CERITHIID®. 
numerous, cingulated; aperture ending in a twisted, short canal. 
Operculum very thin, ‘indistinctly spiral, with excentric nucleus. 
T. granosus, Wood (Ixx, 65). 
PoraMIDEs, Brongniart. 
Etym.—Potamos, a river, and zdes, 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 (1xix, 63). P. ebeninum, Brug. (1xx, 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 anteriorly. Operculum corneous, multispiral. Fluviatile. 
Siam. P. pagodula, 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. (xx, 68). 
LAMPANIA, Gray. Shell turriculated, whorls numerous, without 
varices; sculpture not prominent; aperture truncate below; 
without canal; outer lip sinuous. P. zonale, Brug. (1xx, 69). 
pyrazus, Montfort. (Terebralia, Swains.) Whorls with 
revolving strix, 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. (xx, 70). P. palustris occurs in 
ereat 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 plicze, and opposite to 
these, upon the surface of the outer 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 Nerina, 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 
