Three new genera and eighteen new species of miniature polydesmid millipedes from the northwestern United States (Diplopoda, Polydesmida, Polydesmidae) Author Shear, William A. Professor Emeritus, Department of Biology, Hampden-Sydney College, Hampden-Sydney VA 23943; present address 1950 Price Drive, Farmville VA 23901. Author Marek, Paul E. 0000-0002-7048-2514 Associate Professor, Department of Entomology, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061. pmarek @ vt. edu; https: // orcid. org / 0000 - 0002 - 7048 - 2514 pmarek@vt.edu text Zootaxa 2021 2021-05-24 4975 1 81 126 journal article 6194 10.11646/zootaxa.4975.1.3 529d48db-4299-4e2d-9aaf-6c4178c08b18 1175-5326 4804909 DB7C9028-3EDF-454F-88D0-336624AD1DC4 Retrorsioides Shear & Marek , new genus Type species : Retrorsioides castellum , n. sp. Species included: Retrorsioides castellum , n. sp. , R. linnensis , n. sp. , R. kittitas , n. sp. , R. bammerti , n. sp. , and R. arboramagna , n. sp. Diagnosis. Clearly related to Retrorsia , species of this genus are distinct in the gonopod having a prominent, anteriodorsally directed process at about the level of the pulvillus (absent in Retrorsia species ), and in having a pulvillar process rather than a pulvillar notch (present in Retrorsia species ). Etymology. The name of the genus is based on the similarity of the included species to species of Retrorsia . Distribution. Washington , Oregon and northern California . Notes. Retrorsioides species encompass a wide distribution, from Humboldt Co. in northern California north to Thurston Co., Washington . The general appearance of the species is much like that of Retrorsia species , and the other polydesmids described herein. In addition to the accessory sensory area on the sixth antennal segment, there may also be a small cluster of sensilla near the distal end of the seventh segment. There may be up to 24 setae in the anterior marginal row on the collum, and alveolate cuticle, while present on the anterior part of the collum, is not seen on the dorsa of any of the anterior metazonites. However, the epiprocts of all the species have alveolate cuticle posteriorly. Males have crassate legs and typical (for this group of genera) sphaerotrichomes on the anterior tarsi. In two of the species, the pygidium or epiproct is swollen and curved ventrally, as it is in Snoqualmia species. The gonopod prefemora may be bulbous or small and flattened. The gonopod acropodites are shorter and stouter than in Retrorsia species and are not apically recurved, nor are they distally divided. Instead, a long, acute process arises at about the level of the pulvillus, which is not associated with a semicircular notch, but with a short pulvillar process.