A new species of scincid lizard allied to Plestiodon japonicus (Peters, 1864) was described as P. finitimus sp. nov., fromthe eastern part of Honshu and Hokkaido, Japan. A previous DNA study reported the taxonomic status of the easternJapanese populations of Plestiodon as an undescribed species on the basis of their collective genetic distinctness from aparapatric congener P. japonicus sensu strict from the western part of mainland Japan. We present the diagnostic featuresof P. finitimus compared to P. japonicus and P. latiscutatus Hallowell, 1861, the other parapatric species occurring in theIzu Peninsula and Izu Islands of central Japan, on the basis of morphological characteristics and DNA barcode patterns.Both P. finitimus and P. japonicus have a small postnasal and large anterior loreal that contacts the supralabials. In contrast,the Izu Peninsular populations of P. latiscutatus, which had no known diagnostic features relative to the other two species,usually have a large postnasal and small anterior loreal, with the latter separated from the supralabials by the former, ormay otherwise lack a postnasal. In most populations of P. finitimus, the right and left prefrontals are usually isolated fromeach other, whereas they exhibit medial contact in most populations of P. japonicus. Although all the above characters arevariable both within and between populations, 60–90% of the specimens from each locality on mainland Japan werecorrectly identified using a combination of these characters. Based on these characters, the Russian Far East populationof Plestiodon was also identified as P. finitimus. The interspecific sequence differences in the standard DNA barcoderegion (a 658 base pair fragment of the cytochrome c oxidase subunit I gene of mitochondrial DNA) were distinct, andeach of the three species was exclusively clustered in a neighbor-joining tree. The limited hybridization among the threespecies indicated by previous studies suggests that DNA barcodes could provide a reliable key for their correctidentification. The implications for the biogeography and speciation of the three parapatric lizard species are briefly discussed.