by Robert S. Lemmon ; illustrated by Jean Zallinger by Roberts S. Lemmon; illustrated by Fritz Kredel by Herbert S. Zim; pictures by Jean Zallinger Roy Chapman Andrews; illustrated by Jean Zallinger by Robert Froman; illustrated by Byron Barton by Robert Sidney Bowen; illustrated by Bernard Case by Robert Tallant; illustrated by John Chase by Roberta Edwards ; illustrated by John O'Brien. by Roy A. Gallant; illustrated by John Polgreen by Robert Sliverberg; illustrated by Leonard Everett Fisher