Several generic schemes used in classifying species belonging to Prionospio Malmgren, 1867 sensu lato have been reviewed; three taxa have been retained at the generic level, and three additional taxa at the subgeneric level. The following genera and subgenera are recognized: Prionospio Malmgren, 1867, including the subgenera Minuspio Foster, 1971, Aquilaspio Foster, 1971 and Prionospio Malmgren (sensu stricto); Apoprionospio Foster, 1969, and Paraprionospio Caullery, 1914. Prionospio sensu lato includes species with various combinations of branchiae which are smooth (apinnate), wrinkled, or with digitiform pinnules, beginning on setiger 2. Apoprionospio includes species having branchiae from setiger 2, with at least one pair having plate-like pinnules. Paraprionospio includes species with branchiae from setiger 1, with all pairs having platelike pinnules. Fifteen species, including seven new species, belonging to the genus Prionospio are described. Prionospio (Prionospio) steenstrupi Malmgren, 1867 is described from the syntype series, and is newly synonymized with P. fallax Soderstrom, 1920. The validity of P. bocki Soderstrom, 1920 as a separate species is discussed, as is the indeterminable nature of P. malmgreni Claparede, 1869. Prionospio (Prionospio) dubia Day, 1961 originally described as a new variety of P. malmgreni from S Africa, is raised to full species status. Prionospio (P.) cristata Foster, 1971 and P. (P.) heterobranchia Moore, 1907 are redescribed. Prionospio (P.) tripinnata, a new species with three pairs of pinnate branchiae, is described from the Mediterranean Sea and compared with P. plumosa Sars, 1872. A new synonymy is proposed for P. lobulata Fauchald, 1972 with P. (P.) ehlersi Fauvel, 1928. Two new species, P. (Minuspio) fauchaldi and P. (M.) laciniosa, are described in which the apinnate branchiae are distinctly wrinkled or sculptured, rather than smooth. P. (M.) laciniosa is also distinguished by dorsal crests modified into semicircular flaps. Several species previously referred to Prionospio (Minuspio) cirrifera Wiren, 1883 are reviewed and described. The seven species recognized by Foster in the genus Minuspio are considered; several are retained, and new species and new synonymies are proposed. Because the types are apparently lost, a description of P. (M.) cirrifera is given based on specimens from near the type locality. Prionospio (M.) aluta new species is separated from P. (M.) cirrifera on the basis of the presence of lateral pouches in P. aluta and their absence in P. cirrifera. Prionospio (M.) delta Hartman, 1965 is retained as a valid species; P. (M.) longibranchiata Reish, 1968 and P. (M.) minor Fauchald & Hancock, 1981 are newly synonymized with P. delta. P. (M.) multibranchiata Berkeley, 1927 is also retained as a valid species, and P. (M.) perkinsi, P. (M.) lighti and P. (M.) wireni are newly described from shallow water. Two species are recognized as belonging to Apoprionospio Foster: A. pygmaea (Hartman, 1961) and A. dayi Foster, 1969. New records and range extensions are given for both species. New records are also presented for Paraprionospio pinnata (Ehlers, 1901).
