A cichlid species first collected by Alfred Russell Wallace in the upper Rio Negro in 1852, lost during the transport to England but documented in drawings, is described as Crenicichla monicae on the basis of three specimens collected by the Swedish Amazonas Expedition 1923–1925. Crenicichla monicae is most similar to C. johanna, C. rosemariae, and one undescribed species which are characterized by cycloid scales, distinguishing them from other species of the genus in which most scales are ctenoid. Crenicichla monicae is recorded only from the lower Rio Uaupés and lower Rio Içana, tributaries of the upper Rio Negro, and is sympatric with the similar species C. johanna and C. lenticulata. It is distinguished from all other species of Crenicichla by the color pattern in females, with scattered dark spots on the upper half of the side and on the dorsal and caudal fins. Crenicichla monicae is a member of the C. lugubris species group, characterized by very small scales in a large number along the middle of the side (89–126 scales in E1 row), blunt snout, and particular ontogenetic transformation of color pattern.