A second study of the testate amoebae of the region of Porto Alegre, Rio Grande do Sul revealed the presence of Arcella Ehrenberg, 1830.Difflugia Leclerc, 1815, Lesquereusia Schulumberger, 1845, Centropyxis Stein, 1857, Bulinularia Penard, 1911 and Euglypha Dujardin, 1841 genera. Our finds demand emendations of the diagnostic characteristics of several species.

The natural formation of gas vacuoles as a method of locomotion is described for Difflugia mitriformis Wallich, 1984. These vacuoles may contain different compositions of gases, basicly carbodioxyde or oxigen, with a membranous limitation similar or identical to other types of vacuoles. Those vacuoles are utilised by the organism as a mode of dislocation frorn the bottom to the water surface by flotation permiting better conditions for the survival of the individual, with the consequence of the perpetuance of the taxon.

This paper reports feeding habitats, most commom test constitution, and growing curvature obtained under cultivation conditions, and the knowing distribution and most commom Difflugia lobostoma.