On some brackish Water Mollusca from the Lake of Maracaibo

INTRODUCTION The Lake of Maracaibo, situated in the northwestern part of the Venezuelan Republic, occupies the centre of a large topographical and structural depression between the Colombian Andes on the west and the northeast trending Venezuelan Andes on the south and east. It is a flask-shaped body of water, measuring about 200 kilometers from north to south and its width varies from about 100 kilometers in the south to less than 10 kilometers between the City of Maracaibo and the village of Altagracia. Though it has an open connection with the Caribbean sea through the Gulf of Venezuela, the water of the Lake is almost fresh on account of the many rivers emptying into it from the mountains to the south, west and east. North from Maracaibo, however, where the Lake empties into a small bay, called the Bay of Tablazo, the water changes gradually from slightly brackish to more saline. The water in this part of the Lake is extremely shallow because of filling in with sediments and only one deep and narrow channel running between the Peninsula of San Carlos and the Isle of Zapara allows medium sized ships to reach the City of Maracaibo. Hedberg (1934) investigated the occurrence of recent foraminifera in the lake waters and recognized a number of brackish and shallow water species. He points out that the salinity of the water of the Maracaibo Strait and the Bay of Tablazo is variable, because especially during the rainy season a considerable quantity of fresh water finds its way into the Gulf of Venezuela through the Maracaibo Strait. On the other hand, semidiurnal tides may affect the salinity of the northern part of the Strait to some extent. Analyses of the lake water from Maracaibo and vicinity, however,