A series of 36 specimens of Geochelone carbonaria from the provinces of Darien and San Blas, Panama, definitely establishes the occurrence of that species in Panama. A population on Isla Pinos (San Blas group) may or may not be natural. The closely related species G. denticulata does not occur in Panama and seems not to occur west of the Cordillera Oriental of Colombia. Geochelone carbonaria prefers a dense forest habitat; although the species is hunted for food, it seems to survive in areas of human population. A detailed description of color, includingf ontogenetic changes, is given. Sexual maturity is attained probably at lengths of 200 to 250 mm. Clutch size is estimated to be 8 to 13 eggs, and length of hatchlings is estimated to be 53 mm. Variation is discussed in some detail, especially for characters which are used to diagnose the species G. carbonaria and G. denticulata. Sexual dimorphism is most evident in shape of shell; old individuals of both sexes have shells which are indented below and constricted about the middle, but the condition is more extreme in males. Shape of shell and head scalation are shown in diagrams. Williams (1960:120) has demonstrated, that two species of tortoises (Geochelone denticulata and G. carbonaria) inhabit northern South America. The two species resemble each other closely and are probably closely related. According to Williams (1960:2), they can be taxonomically separated with ease by using a series of characteristics (shape and texture of shell, color, and scutellation). Using these characteristics, I have found populations of Geochelone in Panama to be clearly referable to carbonaria. The following remarks, based on a total of 38 specimens (including a series of 35 from a small geographic area), provide new information on G. carbonaria at or near the extreme northwestern limit of its geographic range.