A new subspecies and a new species are described: Monolistra (Monolistra) caeca meridionalis nov. subspec. was found in three caves in the northern part of Croatia, Yougoslavia. It is distinguishable from the typical form principally by the thin, acuminate form of the protuberance of the protopodite of the 2nd male peraeopod, by the endopodite of the 1st pleopod which bears 3-4 setae (1-2 in M. c. caeca), by the somewhat wider endopodite of the 3rd pleopod and by the shorter, only slightly curved uropods. A sketch shows the situation of 6 newly discovered localities in northern Croatia, 3 of the typical form and three of the new subspecies. Microtistra sketi is the 6th species known of its genus and lives in a cave, in stagnant water of a periodic spring, tributary to the river Gacka in Croatia. The number (three pairs), and the length of the spines of the carapace and the pointedness of the epimers of the pereion are intermediate between those of the spiny forms living in Slovenia and the tubercular species M. pretneri Sket from Dalmatia and M. schottlaenderi (Stammer) from the vicinity of Trieste.