Open Access

Rowland M. Shelley, Jamie M. Smith

• Ptyoiulus Cook 1895, the dominant parajulid diplopod genus in the eastern United States (US), comprises two species – P. impressus (Say 1821), with a slanted, fl ared, circumferentially entire, and marginally serrate apical calyx on the anterior gonopod coxal process, and P. montanus (Cope 1869), n. comb., with a smooth, upright, cupulate calyx that is open caudad and coaxial with the process’ stem. The genus occupies a broad area between the Mississippi River and Atlantic Ocean extending from southern New England, Ontario, and Michigan to the Florida Panhandle and four small disjunct ones – from Montreal, Québec, to northern Vermont, along southwestern Lake Michigan in Wisconsin and Illinois; northeastern/eastcentral Arkansas, primarily in Crowley’s Ridge physiographic feature and beside the “bootheel” of Missouri; and a point locality in northeastern Louisiana just south of the Arkansas line. A male from Chester County (Co.), Pennsylvania, is designated as the neotype of Julus impressus, as is one from Durham Co., North Carolina, for J. montanus. As both species inhabit Montgomery Co., Virginia, the type locality of J. montanus, we exercise the right of first reviser, conserve the latter name, and assign it to the species with the smooth, cupulate, and coaxial calyx. We also exercise first reviser rights and assign Parajulus ectenes Bollman 1887 to this form, thereby relegating it to synonymy under Ptyoiulus montanus. Other new synonymies include Ptyoiulus georgiensis Chamberlin 1943 under P. impressus and P. coveanus Chamberlin 1943 under P. montanus. Both Ptyoiulus and P. impressus are projected for Delaware and Rhode Island and newly reported from Québec, Connecticut, District of Columbia, Maryland, Mississippi, South Carolina, Vermont, West Virginia, and Wisconsin, and the genus and species, respectively, are newly documented from Louisiana and Arkansas; P. montanus is newly cited from Alabama, Arkansas, Georgia, Mississippi, and South Carolina. Ptyoiulus impressus occupies every state except perhaps Louisiana and is the only species in areas that were inundated during the Cretaceous and glaciated during the Pleistocene; by contrast, P. montanus inhabits a relatively narrow east/west transect through the center of the generic range. Their distribution patterns suggest an old species, montanus, being actively displaced by the younger and more successful impressus. The decurvature of the epiproct in uroblaniulinines appears to increase with age and developmental stage. A key is presented to parajulid familygroup taxa in the US and Canada east of the Rocky Mountains.