ABSTRACT: Based on morphological and molecular characteristics, we describe a new genus and species of monothalamous agglutinated foraminifera, Capsammina patelliformis, that occurs mainly at bathyal (1000-3400m) water depths in the Nazare Canyon off Portugal. The test is strongly flattened, up to 500µm or more in maximum dimension, and 30-80µm thick. It lacks obvious apertures, and is typically composed of 2-3 large, plate-like grains of mica that form the upper and lower surface of the test; these are separated by fine-grained, white agglutinated material ("mortar") forming a ring around the cell body. The cytoplasm, visible through the mica plates, is whitish in colour with few obvious inclusions. Analysis of a fragment of the SSUrDNA gene indicates that C. patelliformis belongs in a clade branching with Crithionina delacai, C. granum and an undetermined crithioninid species. However, the divergences between the new species and these Crithionina species range from 20% to 21%, and are therefore too high to classify it in the same genus. We also transfer a previously described species, Psammosphaera bowmanni Heron-Allen and Earland 1912, to Capsammina based on its use of mica flakes in test construction. Other monothalamous agglutinated foraminifera, including Psammosphera spp., are phylogenetically distant from Capsammina. The new species occupies a shallow infaunal microhabitat, living mainly in the top 0.5cm of sediment.