162 BULLETIN 180, UNITED STATES NATIONAL MUSEUM 



115162, Hull Island channel, July 7-17, 1939, 4 specimens. 



115165, Enderbury Island reef May 15-19, 1939, 3 specimens. 



115166, Hull Island reef, July 13, 1939, 6 specimens. 



52505, Pago Pago, Samoa, Jordan and Kellogg, 3 specimens. 



The following counts and measurements, expressed in hundredths 

 of the standard length, were made on three specimens : 155, 157, and 

 70 mm., respectively; depth 58, 59.6, 61.0; head 31.4, 31.8; 35.3; snout 

 23.2, 24.8, 25.0; eye 8.1, 7.8, 10.9; mouth 6.2, 7.3, 7.4; postorbital part 

 of head 4.8, 4.8, 5.0; least depth caudal peduncle 11.0, 11.0, 10.9 ; distance 

 base last anal ray to base midrays caudal fin 11.0, 10.2, 10.7; length 

 of caudal spine 11.0, 10.8, 7.1; interorbital 9.7, 10.1, 11.0; dorsal rays 

 IX, 30; IX, 30 ; IX, 30. Anal rays III, 27; III, 27 : III, 27. Pectoral 

 rays I, 15; I, 15; I, 15. Gill rakers first arch 5+13; 5 + 13; 5 + 14. 

 Teeth on upper and lower jaw 10+ 10 ; 10+ 12 ; 8 + 10. 



ACANTHURUS ACHILLES Shaw 



Acatithurus achilles Shaw, General zoology, vol. 4, p. 383, 1803. 



115139, Swains Island reef, May 3-9, 1939, 16 specimens. 



115140, Enderbury Island leef, May 15-19, 1939, 8 specimens. 

 115138, Hull Island reef, July 12-15, 1939, 2 specimens. 



115141, Hull Island channel, July 7-17, 1939, 1 specimen. 

 115137, Rose Island reef, June 11-14, 1939, 20 specimens. 

 52475, Apia, Samoa, Jordan and Kellogg, 1 specimen. 



A careful comparison of my numerous specimens of several sizes 

 with plate 77 of Gunther's Acanthurus aterrimus indicates conclu- 

 sively to me that it is a young specimen of this common species. 

 With age the caudal fin becomes less lunate and the red caudal spot 

 develops. 



ACANTHURUS TRIOSTEGUS (Linnaeus) 



Chaetodon triostegus Linnaeus, Systema naturae, ed. 10, p. 463, 1758. 



On May 24, 1939, in Canton Island lagoon, this species was in 

 breeding colors. On males the margin of the anal was white; the 

 vertical stripes were dark purj^le; margins of pel vies white; fins 

 dusky, and the general background color olive green tinged with 

 blackish. A gentle pressure on some of the males caused the milt to 

 flow freely. During the next month females with almost ripe eggs 

 were frequently found. 



115151, Canton Island, lagoon, May 25-26, 1939, 1 specimen. 



115128, Tau Island, reef at Siulagi Point, June 27, 1939, 6 specimens. 



115116, Canton Island, lagoon, April 23 to May 12, 1939, 6 specimens. 

 115115, Canton Island, reef on ocean side, April 2.5-28, 1939, 37 specimens. 

 115114, Canton Island, reef in wide channel. May 13, 1939, 24 specimens. 



115117, Canton Island, lagoon coral heads, May 28-25, 1939, 2 specimens. 

 115127, Swains Island reef. May 3-9, 1939, 7 specimens. 



115124, Enderbury Island reef. May 15-19, 1939, 85 specimens. 



115121, Tutuila Island, Fagasa Bay, rock pools, June 5, 1939, 2 specimens. 



