A survey was made of the yeasts occurring in the intestinal tract of wild species ofDrosophila occurring in the Yosemite Region of California. Two hundred and forty one yeasts, representing 42 species and varieties, were identified. Each isolate was obtained from a different fly. Almost half of the isolates belong toSaccharomyces. The most common species in this genus wereS. montanus (36 isolates),S. veronae (30 isolates),S. cerevisiae var.tetrasporus (22 isolates) andS. drosophilarum (13 isolates). Further species are listed in Table 1.Zygosaccharomyces fermentati Naganishi was shown to be a distinct species and not a synonym ofS. cerevisiae. In order to avoid confusion with another yeast of the same name, it has been proposed to change the nameZ. fermentati toS. montanus Naganishi. Two new species ofSaccharomyces were described,S. wickerhamii andS. kluyveri. S. mangini var.tetrasporus has been renamedS. cerevisiae var.tetrasporus. A non-cellobiose attacking strain ofS. drosophilarum has been designated tentativelyS. drosophilarum var.acellobiosa. A new species of the genusPichia was described asP. xylosa. Saccharomyces pastori andSaccharomyces pini were transferred to the genusPichia on the basis of arguments given in the preceding paper. A new species ofTrichosporon was described asTr. aculeatum on the basis of the presence of characteristic needlelike cells. Common species besides those mentioned inSaccharomyces wereHansenula angusta (19),Kloeckera apiculata (15),Kl. magna (13), andTorulopsis stellata (10). Other genera represented wereHanseniaspora, Cryptococus, Rhodotorula, Candida andOospora. Evidence was obtained that many species of imperfect genera consist of distinctly different physiological types.
