164 BULLETIN 1.8 0, UNITED STATES NATIONAL MUSEUM 



Length of mouth, from tip of snout to rear of maxillary 6.6 (6.7; 

 8.0). Postorbital part of head 4.7 (5.2; 5.6). Length of longest 

 pectoral fin ray 29.5 (28.5; 35.1). Length of longest dorsal spine 

 16.0 (14.9; 18.9). Length of longest dorsal soft ray 16.7 (16.1; 21.4). 

 Length of longest caudal fin ray 30.0 (27.3, 34.5). Longest pelvic 

 ray 21.3 (21.6; 23.9). Length middle caudal fin rays 18.7 (19.3; 

 22.4). Least depth of caudal peduncle 10.5 (10.8; 11.5). Length of 

 caudal peduncle distance from base last anal ray to base of middle 

 rays of caudal fin 10.7 (10.9; 12.1). Length of spine on caudal 

 peduncle 10.3 (10.3; 7.1). Width of interorbital space 10.3 (10.4; 

 11.1). Length of base of anal fin 45.3 (44.7; 47.2). Length of base 

 of dorsal fin 70.6 (72.1; 70.0). 



Although the small specimen differs considerably in its measure- 

 ments from the adults, it is thought that this is a result of size. 



Dorsal rays IX, 28 (IX, 31; IX, 29). Anal rays III, 27 (III, 27; 

 III, 26). Pectoral fin rays I, 15 (I, 16; I, 15). Pelvic rays I, 5 (I, 

 5; I, 5). Scales very small and the rows irregular but about 125 to 

 130 rows crossing side of body from upper edge of gill opening to 

 base of caudal fin rays. Gill rakers on first gill arch 5 + 12 (5 + 13; 

 5 + 13). Number of teeth in upper and lower jaws 8 + 12 (9 + 10; 

 8 + 10). 



Color (description based on holotype and paratypes) : Ground 

 color black; the spine on the caudal peduncle with a narrow pale 

 area around it; the margin of the dorsal and anal fins with a white 

 line, more distinct j^osteriorly ; at base of rays of dorsal and anal 

 fins is a white line that expands posteriorly to include one-third of 

 the basal portion of the last few rays of these fins, dorsal and anal 

 fins otherwise black; pectorals blackish; pelvics with a white line 

 along their outer margin and rest of fin black; anus pale; U-shaped 

 white band on lower half of jaw, this pale color ending on the pos- 

 terior tips of maxillaries; caudal fin with pale band posteriorly, be- 

 coming narrower on upper and lower lobes, then a brownish diffuse 

 band grading into darker, followed by a submarginal black line, color 

 brownish on basal three-fourths of fin, grading in black at base of 

 rays and on caudal peduncle. No light area below the eye and no 

 white margin posteriorly on the opercle; no second submarginal pale 

 band below the black line on the caudal fin, and the caudal fin not 

 abruptly paler, greatly contrasting with the black caudal peduncle as 

 in A. glauco'paTeius. 



Remarks. — This species differs from all members of the genus Acan- 

 ihurus in regard to the color pattern of the caudal fin, which has a 

 pale marginal band and submarginal black line that follows the out- 

 line of the caudal fin posteriorly. It appears to be most closely re- 

 lated to Acanthurus glaucopareius and the young of A. achilles in its 

 coloration, but the new species lacks the pale blotch below the eye and 



