The fur is soft, woolly, and generally dark. The upper parts are finely mixed olivaceous and dull tawny olive or finely mixed cinnamon buff and black. The underparts, especially along the midline, are markedly orange rufous. The ears are short, and there is a well-defined central groove on the upper incisors of some specimens.
Females have six mammae.
This kind of squirrel was unknown even to the native hunters who accompanied the collector. Syntheosciurus now has been observed at elevations up to 2,600 meters in undisturbed forest, disturbed forest, shrublands, and pasture edges. Three nests have been found in tree cavities at heights of 6-12 meters. Foraging occurs in the underbrush, in the forest litter, and on the ground. The diet consists mostly of flowers, buds, leaves, and sap.