The Leiobunum calcar species-group is erected to accommodate four species of North American harvestmen, namely, L. nigropalpi (Wood 1868), L. euserratipalpe new species, L. calcar (Wood 1868) and L. hoffmani new species. The group is characterized by several sexually dimorphic characters, including an elongate penis lacking subterminal sacs, base of male palpal tibia projecting ventrally and denticulate, and unique female sterno-opercular mechanism that appears to act as a pregenital barricade. The four species are distinguished by penial and palpal features in the male and by details of the sterno-opercular mechanism in females. The history of confusion between L. serratipalpe Roewer 1910 and L. calcar is reviewed, and the new species L. euserratipalpe is proposed to accommodate the concept of L. serratipalpe developed by North American systematists as well as the synonymy of L. serratipalpe Roewer with L. calcar. All species are diagnosed, described and illustrated, and a key to species is provided.