The Narugo thermal springs locate in northwestern Miyagi Prefecture and consist of as many as 30 sources of springs, which are situated along the river Araogawa. We have 9 spas in the Narugo thermal springs as shown in fig. 1, namely Kawatabi (sulphur), Tanakayu (alkaline), Sin-Tanakayu (bitter), Akayu (alkaline, simple thermal), Motokurumayu (bitter), Sin-kurumayu (bitter), Taganoyu (acid and sulphur), Narugo-Yumoto (sulphur, alkaline, acid and bitter) and Kawarayu (mineral). We have visited these spas twice, in August and October in 1939, and collected many materials which were developed in natural condition. 6 species of Bacteria, 15 species, 5 varieties and 2 forms of Cyanophyceae and 2 species and 1 variety of Chlorophyceae are enumerated. Among them, 2 new forms of Cyanophyeae were described: Phormidiumtenue (MENEGH.) GOM. forma non-constrictum and Symploca thermalis (KÜTZ.) GOM. forma longiarcticulata. Moreover, 3 species and 3 varieties are added as new thermal flora of Japan: Gloeothece rupestris (LYNGB.) BORN., Stigonema tomentosum (KÜTZ.) HIERON., Scytonema caldarium AG., Ph. valderianum (DELP.) GOM. var. tenuis WORONI., Symploca muscorum (AG.) GOM. var. calderiorum LEMM. and Oocystis solitaria WITTROCK. var. elongala PRINTZ.