This work was begun in 1964 and substantially completed in 1965; at that time conodont zones had been established in North America only for the Upper Devonian, by Clark and Becker (1960) for the Great Basin and Collinson, Scott, and Rexroad (1962) for the mid-continent. Little was known of the conodonts of the New York section; there was almost no information on the Lower Devonian succession, and there was no published account of the Middle Devonian succession. The present manuscript was submitted for publication in mid 1967, at a time when Devonian conodont biostratigraphy was making very rapid progress. A wealth of information has [since] become available, especially in the volumes of the International Symposium on the Devonian System, Calgary, 1967 (published in 1968). Reference to the more important recent work that bears on the interpretation of the biostratigraphy of the Llano region is included herein, but a complete revision has not been attempted [February 1969].