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PACIFIC SCIENCE, VoL IX, October, 1955 
shaped brush-like patch of setae on sides, 
very prominent in larger specimens where it 
extends nearly half way to the base of the 
pectoral fin from the caudal spine (this velvet- 
like region first becomes apparent in speci- 
mens of 65 to 70 mm. in standard length). 
Color (in alcohol) brown with numerous, 
thin, light gray, irregular, horizontal lines on 
the body which are broken into discrete spots 
anteriorly and on head; on small specimens 
(about 45 to 65 mm. in length) the lines are 
entirely broken up on the body. Specimens 
smaller than 45 mm. have narrow vertical pale 
lines on the body between which spots are 
aligned vertically. In most specimens, regard- 
less of length, a dusky white band of about 
the diameter of a pupil of eye in width extends 
posteriorly from a point just behind the upper 
edge of the gill opening over half the distance 
to the caudal spine. Sheath of caudal spine 
white; median fins brown; pectoral fin mem- 
branes hyaline, rays light brown; upper edge 
of unbranched pectoral ray with a narrow 
black line. 
Color (in life) dark brown, yellowish brown 
anteriorly, with numerous, narrow, wavy, 
light blue longitudinal lines on the body, 
breaking up to small blue dots on nape, chest, 
and head (no linear pattern being evident on 
the latter) ; all fins except pectorals dark 
brown; pectorals clear with dusky orange rays 
and a narrow black upper margin. This color 
note was obtained from an 88 mm. specimen 
collected by me from a recess in a stand of 
dead staghorn coral in the lagoon of Onotoa 
Atoll, Gilbert Islands. 
Although colors of olive or dark green and 
black have been given for the species, the 
majority of the records of the basic life color 
are brown. The other colors may represent 
variability which is possible in individual 
specimens. Other acanthurids are known for 
the ability to alter their hues (Townsend, 
1929). Ctenochaetus striatus (Quoy and Gai- 
mard), also a brown, blue-lined species, may 
appear almost black or distinctly olivaceous 
when alive. 
The young of Z. scopas and Z. veliferum are 
compared in the upper figure of Plate 1. The 
photograph is of fresh specimens captured at 
Onotoa Atoll. 
Schultz and Woods (1953: 642) reported 
that this species was found in or close to deep 
water in the Marshall Islands. I observed 
adults in about 8 feet of water in the Onotoa 
lagoon and on the lee reef of Butaritari Atoll 
in the Gilbert Islands; however, they were 
seen infrequently. 
The largest specimen in the museum ma- 
terial which I have examined measured 149 
mm. in standard length. 
Varied opinions as to the relationship of 
Z. scopas and flavescens have been expressed in 
the literature. 
Gunther (1873: 117) united Acanthurus 
rhombeus (= Z. scopas ) with flavescens , regard- 
ing the yellow form in Hawaii as probably a 
case of albinism. Jordan and Seale (1906: 355) 
(1907: 34) stated that the two are probably 
the same species, though they retained both 
names. Herre (1927: 443), Fowler and Bean 
(1929: 260), Aoyagi (1943: 204), Schultz and 
Woods (1953: 152), and others have asserted 
their belief that these are color forms of a 
single species. Jordan and Fowler (1902: 556) 
wrote, "Probably the typical flavescens is found 
in deep water, the variety rhombeum living near 
shore.” Certainly this does not seem to be 
true, for neither form appears restricted to any 
particular depth on the reef. I have observed 
Z. flavescens in Hawaii in from about 3 to 90 
feet of water. Z. scopas (as here defined) is 
known from Zanzibar to southern and western 
Oceania. In spite of extensive collecting and 
underwater observation in the Hawaiian Is- 
lands, Johnston Island, and Wake Island by 
W. A. Gosline, V. E. Brock, myself, and 
others, no specimens of Z. scopas (the so called 
brown phase of Z. flavescens ) have been seen, 
although the bright yellow Z. flavescens is 
abundant. The few museum specimens from 
Marcus Island and Guam are pale, presum- 
ably yellow in life, and hence Z. flavescens. 
