156 BULLETIN 18 0, UNITED STATES NATIONAL MUSEUM 



52506, Pago Pago, Samoa, Jordan and Kellogg, 5 specimens. 



56994, Pago Pago, Samoa, 3 specimens. 



82945, Samoa, Wilkes Exploring Expedition, 3 specimens. 



Family ACANTHURIDAE 



KEY TO THE GENERA. AND SPECIES OF ACANTHURIDAE FROM THE PHOENIX 



AND SAMOAN ISLANDS 



la. Tail armed witli a single sharp, antrorse, erectile spine, fitting into a groove ; 

 caudal spine often obsolete in young specimens. 

 2a. Teeth long, movable, on pedicels or bristlelike, expanded at tips or with 

 cupped denticulate tips, about 36 to 40 in upper jaw and 3S to 46 in 

 lower jaw; dorsal rays VIII (rarely IX), 28 to 30; anal rays III, 2G 

 or 27; pectoral I, 16, pelvic rays I, 5; gill rakers about 9 to 11+21 to 23; 

 ground color blackish, sides of body with faint purplish or bluish wavy 

 lines ; all fins blackish ; caudal fin lunate. 



Ctenochaetus strigosus (Bennett) 

 2&. Teeth immovable, not on long pedicels, but broad, lobate, and fewer than 

 30 in upper or lower jaws ; pelvic rays I, 5. 

 3a. Dorsal spines IX, rarely VIII or X. 



4a. Posterior or lower margin of operculum with a white band or area 

 that occurs in specimens with regularity down to at least 60 mm. in 

 standard length ; ground color of head and trunk blackish. 

 5a. A pale blotch below eye, upper posterior margin of opercle with a 

 narrow white band; lips pale with a U-shaped band on lower 

 side of chin extending much above maxillaries ; spine on caudal 

 peduncle pale but area around it black ; margin of dorsal and 

 anal fins wliite, rest of fins blackish except along their bases a 

 white line widens posteriorly to include two-thirds to three-fourths 

 of basal portion of fins ; pectorals dusky ; pelvics black with their 

 outer margin pale ; anus pale ; caudal fin pale-dusky but abruptly 

 paler than caudal peduncle, margin of caudal fin white, then a 

 wide dusky submarginal band, followed by a narrow pale band, 

 basal two-thirds of this fin pale-dusky, sharply contrasting with 

 black caudal peduncle; dorsal rays about IX, 30; anal rays III, 

 27 or 28; pectoral 1, 15; teeth about 8 to 10+10 to 14. 



Acanthurus glaucopareius (Bloch) 

 5&. No pale area below eye; lower posterior corner of operculum with 

 a wide area or spot ; lips and body blackish ; a U-shaped band 

 on lower side of chin extending up to maxillaries ; in adults an 

 oval light area, yellowish in alcohol, red in life, posteriorly on 

 body and including spine on caudal peduncle, but this charac- 

 teristic light area not developing until fish has reached a length 

 of about 65 to 70 mm. (thus Giinther's A. atcrrbnus becomes a 

 synonym of A. achUles) ; along posterior base of soft dorsal and 

 anal a pale line, blue in life, and on base of rays a narrow red 

 band; margin of caudal fin yellowish (red in life), then a sub- 

 marginal black band that follows outline of edges of entire 

 caudal fin and encloses a central yellowish (red in life) area, 

 absent on specimens 70 mm. and shorter; color in fins not ap- 

 pearing until a length of about 60 to 65 mm. is attained ; dorsal 

 rays IX, 30 to 34; anal III, 28 to 30; pectoral I, 16; teeth 

 about 8 + 10 ; gill rakers 5 or 6 + 12 to 14. 



Acanthurus achilles Shaw 



