Blooper

Doug McClure's character remains clean shaven throughout the film, even though he had no access to shaving utensils.

The guards in front of the White House are dressed in British police uniforms.

The human females all have shaved legs which seems implausible in their environment.

When David and Perry escape from the Mahar city and find Dia threatened by a fire breathing creature, David attempts to protect Dia by putting himself between her and the creature. In a matter of a minute or so, Perry miraculously shoots the creature with a bow and several arrows, with no explanation where they came from. ------- Correction: After the three meet up, he explains he used the string/chord from his glasses for the bowstring, and the David's axe came in handy, too (presumably, to assist in cutting something for the bow and arrows).

The Pellucidarians live in a Jurassic type environment and are not far above Neanderthals on the evolution scale, yet they have perfect cylindrical shaped arrows and steel hatchets.

When David is fighting the prehistoric lizard with a spear, he is pushed by the (slowly and awkwardly) charging lizard into the throng of other prisoners. The dark-haired woman behind David can be seen not looking startled or scared at all, and is actually suppressing a grin.

The film never explains why the Pellucidans speak English; indeed, David doesn't even seem surprised.