A new genus of anilline carabid beetle, Medusapyga LaBonte and Maddison, is described from the Pacific Northwest. Two new species, herein described, comprise this genus. Members of the genus are distinguished from other described North American Anillini by: an extensive field of long bifurcate setae on each laterotergite IX of females, a distinct ventrobasal spine on the male profemur, and two strongly asymmetrically dilated and ventrally setose basal protarsomeres in males. Bifurcate setae on the laterotergites have not previously been described for any carabid beetle. A more restricted field of shorter bifurcate setae is also present in the Californian anilline genus Anillaspis Casey, which we infer to be the sister of Medusapyga. A molecular phylogenetic analysis based upon eight gene fragments (two nuclear ribosomal genes, five fragments of nuclear protein-coding genes, and a mitochondrial gene) demonstrates the distinctiveness of Medusapyga, and places it in a clade with the other genera from the United States. The sister group of Medusapyga + Anillaspis is the Californian genus Anillodes Jeannel. Medusapyga alsea LaBonte, the type species of the genus, is known only from three proximate localities in the Oregon Coast Range southwest of Corvallis in western Oregon. Medusapyga chehalis LaBonte is known only from four proximate localities in the Black Hills southwest of Olympia in southwestern Washington state. These are the first species of Anillini described from the Pacific Northwest. Details of habitat and natural history are provided.

Extracted DNA was subjected to PCR, and the products Sanger sequenced. Maximum likelihood analysis was conducted using IQ-TREE.