Dorsal spines (total): 9; Dorsal soft rays (total): 10; Anal spines: 3; Anal soft rays: 7; Vertebrae: 25. This species is separable from all other species of the genus, except S. berryi, by the following combination of characters: segmented rays in anal fin 7, tubed lateral-line scales 50, total gillrakers on first gill arch 35-38 (10 or 11 + 25-27), sum of lateral-line scales and gillrakers on individual specimens 85-88, depth of body 20.6-24.8% SL (4.0-4.9 times in SL), length of depressed anal fin 21.8-23.9 % SL, length of anal-fin base 12.6-14.8% SL, length of first anal-fin spine 3.0-4.8% SL, hypurals 1 & 2 autogenous, hypurals 3 & 4 represented by a single plate, and first caudal vertebra without parapophyses. It can be separated from the Atlantic species S. berryi by a number of morphometric characters. It also differs slightly from S. berryi in counts of pectoral-fin rays (17 or18, mean = 17.33, for S. rhax vs. 16-18, mean = 16.99, for S. berryi).