The book I am interested in is a juvenile / YA science fiction book most likely written in the late 40s or 50s or very early 60s before we landed space probes there. The main character is a boy. They land on Venus and find deserts and no life, but along the way the main character gets lost and finds a valley with dinosaur-like creatures and small primate creatures. Eventually, the primary expedition finds him and all turns out well. I have searched the net but have not found any trace, I checked it our from our public library many times in the 1980s. Thanks!