1927] Pilsbry-Bequaert, The Aquatic Mollusks of the Belgian Congo  QAS 
‘Animal with the rostrum broad, short, and contractile; tentacles wide apart, 
subulate. Eyes on short peduncles united to the outer side of the tentacles. Margin 
of the mantle with a rudimentary siphonal fold in front. Radula long. | 
This family is closely allied to the Melaniide, the above characteriza- 
itons being framed more especially to discriminate the African forms of 
both families rather than to cover the Cerithiide generally. It consists 
mostly of marine forms. A number of genera, however, inhabit brackish 
waters and are often extremely abundant in tropical regions in the river 
estuaries and tidal flats. 
Only one genus is represented at the mouth of the Congo and else- 
where along the West Coast of Africa. It belongs to the subfamily 
Potamidine, a group largely restricted to brackish water, in which the 
shell is usually covered with a brown epidermis and the early whorls of 
the very elongate spire are almost always corroded. ‘The fore part of 
the aperture is more or less channelled, truncate, not produced into 
a beak. The operculum is orbicular, polygyrate, with central nucleus. 
The Potamidinz are more or less amphibious, being able to stand 
prolonged drought, although they breathe exclusively by gills. Of some 
of the species of Cerithidia of the Oriental Region it is said that during 
the dry season they close the aperture with the operculum and hang, 
suspended by glutinous threads, to small branches and mangrove-roots. 
Lang and Bequaert have never observed this with Potamides fuscatus 
of the Congo estuary; that species is found exclusively on the mud of the 
mangrove swamps and tidal flats and was not seen to crawl eS stones, 
roots, or leaves. 
POTAMIDES eee 
Potamides BRoNGNIART, 1810, Ann. Mus. Hist. Nat. Paris, XV, p. 368. Nena: 
type: Potamides lamarki Brongniart, of the Oligocene of France. 
Subgenus Tympanoronos Schumacher 
Tympanotonos SCHUMACHER, 1817, ‘Essai Nouv. Syst. Test.,’ p. 211. Monotype: 
Tympanotonos fluviatilis Schumacher = Murex fuscatus Linneus. 
Tymranostoma G. B. SOWERBY, 1839, ‘Conchol. Man.,’ p: 110. Misspelling of 
Tympanotonos. 
Potamis or Potamides G. B. SowERBY, 1839, op. cit., p. 88. Monotype: Cerithiwm 
muricatum Bruguiére = Murex fuscatus Linneus. 
Tympanotomus Gray, 1842, ‘Syn. Contents Brit. Mus.,’ 44th Ed., p. 90. 
Misspelling of Z’ympanotonos. | 
Tympanotonus Acasstz, 1846, ‘Nomencl. Zool. Index Univ.,’ p. 882. Emenda- 
tion of Tympanotonos. 
In Africa this subgenus occurs on.the western.coast. only,. where it is 
represented by two species, but there are others 1 in the Oriental Region, 
