University of Kansas Publications, Museum of Natural History Editors: Frank B. Cross, Philip S. Humphrey, Robert M. Mengel. Volume 18, No. 6, pp. 505-545, 7 figs., 4 pls. Published December 2, 1969 University of Kansas Lawrence, Kansas PRINTED BY ROBERT R. (BOB) SANDERS, STATE PRINTER TOPEKA, KANSAS 1969 The Systematics of the Frogs of the Hyla rubra Group in Middle America BY JUAN R. LEÓN CONTENTS   Introduction The tree frogs of the Hyla rubra group are abundant and form a conspicuous element