Cytogenetic and morphological studies have begun to reexamine the taxonomy of the red howlers Alouatta seniculus which live throughout the northern and western Amazon basin, in the Guianas, and from northern Colombia and Venezuela, south to Bolivia. We briefly review the current state of knowledge of the taxonomy and distributions of red howlers, in particular, that of the Guianan subspecies. Recently, two names have been applied to populations from this region, Simia straminea Humboldt, 1812, and Alouatta macconnelli Elliot, 1910. Allen (1911, 1916) unquestioningly accepted the validity of A. macconnelli from the Guyana coast, but most subsequent taxonomic revisions (Cruz Lima, 1945; Cabrera, 1957; Husson, 1978) have synonymized it with S. straminea. Tate (1939) and Hill (1962) listed Alouatta seniculus macconnelli, but both doubted its validity. Nevertheless, recent cytogenetic and morphological studies, without due consideration of the taxonomic history of the two scientific names, have led to the resurrection of A. macconnelli, as distinct from S. straminea. The use of the name Alouatta macconnelli has evidently arisen from a cursory reading of Hill (1962) or an uncritical interpretation of his provisional subspecific distribution map or both. There are also contradictory interpretations of a reciprocal translocation as indicating that Simia straminea and Alouatta macconnelli are separate species (Bonvicino et al., 1995) or the same subspecies (Sampaio et al., 1996). Doubts about the type locality of Simia straminea Humboldt, 1812, as given by Hill (1962), led us to research its original description and to conclude that Simia straminea is a synonym of Alouatta caraya and therefore unavailable for Alouatta seniculus. Before A. macconnelli is accepted as the next available name for the Guianan red howlers, however, we advocate a thorough review of Guianan, Venezuelan, and Colombian red howler subspeciation, with due consideration for the taxonomic status of Mycetes auratus and Mycetes laniger Gray, 1845. We note that Alouatta guariba (Humboldt, 1812) is a senior synonym of Alouatta fusca (Saint-Hilaire, 1812).