Distinguished by having an elongated parieto-supraoccipital process, which is broader at base than distally, with its sides converging posteriorly to meet the predorsal plate, and 1.6 to 2.0 times longer than the width of its base. Differs also from other Caribbean sea catfishes by having 3 pairs of barbels, a crescent-shaped predorsal plate, much shorter than the parieto-supraoccipital process, and by lacking a fleshy furrow between posterior nostrils, a fleshy groove in a median depression of the head, and gill rakers on rear surfaces of the first two gill arches. Diagnosed from the eastern Pacific Notarius cookei by having a deeper body, with body depth 20.0-20.5% SL (vs. 17.3-17.9% SL in N. cookei). Attains a larger size of at least up to 8.45 cm TL and has a less exposed and rugose head shield than N. cookei with maximum size of 7.9 TL (Ref. 89868).