Abstract: An attempt is made to clarify the nomenclature of Cystoderma jasonis (Cooke & Massee) Harmaja (C. amianthinum (Fr.) Konr. & Maubl. var. longisporum Kühn.) and the species is compared with the closely related C. amianthinum. It has cyanophilic spore and basidium walls and binucleate spores, and is common in Finland. C. amianthinum was found to have dextrinoid and cyanophilic sclerobasidia. Cystoderma lilacipes Harmaja (C. ‘longisporum (Kühn .) Heinem. & Thoen’ var. purpurascens Heinem. & Thoen, nom. inval.) is compared with the closely related C. jasonis. Hitherto the species has been known from one Belgian locality only; now 12 localities are reported from Finland. Cystoderma tuomikoskii Harmaja and Cystoderma intermedium Harmaja, two new species closely related to C. fallax Smith & Sing., are described on the basis of Finnish material. Cystoderma terreii (Berk. & Broome) Harmaja is regarded as the legitimate name for C. cinnabarinum (Seer.) Konr. & Maubl. The author agrees that the genus Cystoderma Fayod should be placed in the family Tricholomataceae. Some author citations are corrected.