1927] Pilsbry-Bequaert, The Aquatic Mollusks of the Belgian Congo 565 
here together with brackish water species. Thus, along the inner shore 
of Banana Peninsula one finds in company with Neritina adansoniana, 
Lanistes intortus, L. adansoni, Iphigenia curta and I. rostrata, a number 
of other bivalves [Tagelus angulatus (Sowerby), Tellina ampullacea 
Philippi, Lorzpes contrarius (Dunker), Corbula sp., ete.] and snails 
[Haminea sp., Thats coronata (Lamarck), Dorsanum fuscum (Craven), 
Natica marochiensis Gmelin, ete.].1 
Melampus liberianus Potamides fuscatus 
Neritina glabrata Pachymelania aurita 
) adansoniana “4 fusca 
o oweniana Iphigenia curta 
Lanistes intortus rostrata 
Be adansona Cyrenoida senegalensis 
Syncera hesser Congeria ornata ~ 
The most characteristic mollusks of the mangrove area are the 
melanians (Pachymelania) and certain Cerithiidee (Potamides), which in 
some places occur in profusion. Some idea of their fabulous numbers 
may be gained from the photographs reproduced in Pl. LX XVII. Figure 
1 represents a colony of live Potamides fuscatus in the interior of the island 
Bulabemba. This picture was taken in July, 1915, when the shallow 
lagoons in which these snails occur had been for several weeks above 
the level of high tide and thus gradually dried out. The snails then slowly 
migrate toward the lowest and more humid portions of the lagoon; 
during the hottest hours of the day, when they are exposed to the blazing 
rays of the sun, they turn their shells continually, evidently to better 
withstand the heat. At night they get a new supply of moisture through 
the hygroscopic action of the salt that covers the shell and absorbs the 
dew. The operculum is retracted far inside the aperture, which, however, 
is kept moist by a continuous discharge of liquid. Figure 2 of the same 
plate is a closer view of part of the colony shown in Figure 1. When con- 
ditions become still drier, as was observed in nearby spots at Bulabemba, 
Potamides fuscatus digs in the moist, salty mud as deep as one inch 
below the surface, so that hardly an outward trace of their presence is 
visible. Some of the very largest specimens were thus dug up by Mr. H. 
Lang from completely dried out lagoons. 
Pachymelania fusca prefers the quiet mud flats of the mangrove 
swamps, at the margin of the more shallow creeks, which are regularly 
covered and uncovered by the tide, a habitat they share with the multi- 
1The names of marine mollusks here cited are only provisional as the marine fauna of the mouth 
of the Congo has not yet been studied by us. Some of the species have been designated under a variety 
of names and this remark especially applies to the mangrove oyster and Mytilus. 
