Thyrornectria denigrata (Wint.) Seaver,* a Hypocreaceous fungus, occurring on branches and fallen trunks of Gleditschia triacanthos L. in the eastern and central United States, consists of an internal mycelium producing subimmersed or erumpent-superficial, pulvinate, orange-brown stromata. On or near the surfaces of such stromata are formed dense cespitose, carnose-melnbranaceous, subglobose, ostiolate, reddish-brown to black perithecia. The cylindrical, short stipitate asci contain eight hyaline or slightly yellowish short elliptical ascospores which are three to five septate, muriform, more or less constricted at the septa and 10--16 × 7--10μ. This study is based on numerous collections made intermittently in the flood-plain areas around Lincoln, Nebraska, since 1930. Early collections were the source of eighteen monascospore cultures. Slides were made from naturally developed infections and from inoculated materials. The best slides were obtained with materials fixed in formal-acetic-alcohol, cleared in cedar oil, sectioned at three to six microns, stained with Haidenhain\u27s haematoxylin and counter-stained with Orange G. Agar film growth was stained with methyl blue in lactophenol. Zeiss apochromatic lenses have been used in the major part of the microscopic study; sketches have been made with the camera lucida. *Seaver, F. J. (Mycologia 1 : 203--206. 1909) regards Pleonectria Sacc. (Nuov. Giorn. Bot. Ital. 8 : 178. 1876) as synonymous with Thyronectria Sacc. (Grevillea 4; 21, 1875)
