Desert agama (Trapelus pallidus ) is a fairly small agama species (about 20 cm long).
The overall appearance looks rather clumsy, but on closer inspection one notices the long tail – longer than the entire body.
The species is found throughout the Negev and the Arava, in a fairly open landscape, and over the past decades its distribution has been shrinking due to habitat destruction, and it appears to have disappeared entirely from areas in the northwestern Negev.
Sinai agama (Pseudotrapelus sinaitus ), by contrast, is an agama with a slimmer and more elongated overall build, and its distribution is more limited to eastern desert areas (mainly along the Rift).
While the desert agama tends to stay close to the ground and rely on its camouflage when it is spotted, the Sinai agama usually flees quickly.
When the agama is clearly visible, distinguishing between the two species is very easy, but since the observation is sometimes brief and partial, another clue can be used:
In the desert agama, the longest of the toes is the fourth, whereas in the Sinai agama it is the third toe, which gives the foot a more symmetrical structure.

Sinai agama. The third toe is the longest of the toes © אביעד בר

Desert agama. The fourth toe is the longest of the toes © איל ונונו