62 U.S. NATIONAL MUSEUM BULLETIN 202 Vol. 2 



DASCYLLUS ARUANUS (Linnaeus) 



Plate 80, B 



Chaetodon aruanus Linnaeus, Systema naturae, ed. 10, p. 275, 175S (type locality, 

 Indies) . 



SPECIMENS STUDIED 



Bikini Atoll: 11 stations, 192 specimens, 7 to 35 mm. in standard length. 



Eniwetok Atoll: 2 stations, 34 specimens, 23 to 60 mm. 



Rongelap Atoll: 9 stations, 147 specimens, 10.5 to 54 mm. 



Rongerik Atoll: 2 stations, 2 specimens, 37 to 40 mm. 



Likiep Atoll: 1 lot, Imiv. of Washington, 37 specimens, 23 to 58 mm. 



Guam: 6 lots, 88 specimens. 20 to 53 mm. 



Saipan: 2 lots, 30 specimens, 6.5 to 39 mm. 



Description. — Dorsal fin rays XII, 12; mial rays 11,12 or 13; pectoral 

 rays ii,15 or 16; scale rows from upper ed^e of gill opening to base of 

 caudal rays 26 to 29, from base of dorsal to lateral line 4, from lateral 

 line to origin of anal 10; gill rakers 6 or 7 + 1 -+-15 to 17, totaling 23 

 or 24. 



Depth of body 1.5 to 1.7; head 2.6 to 4.0; both in standard length. 

 Snout 3.15 to 5.2; eye 2.4 to 3.0; preorbital width 6.6 to 6.7; upper 

 jaw 3.2 to 3.4; postorbital part of head (hind margin of eye to upper 

 edge of gill opening) 2.75 to 3.4; interorbital width 2.6 to 2.95; depth 

 of caudal peduncle 1.9 to 2.1 ; length of pectoral fin 1.1 to 1.2, of pelvics 

 0.8 to 0.9, of 3rd dorsal spine 1 .4 to 1.9, of upper caudal ray 0.8 to 1.0; 

 all in length of head (tip of snout to posterior tip opercular spine). 

 Depth of caudal peduncle in its length 1.0 to 1.9; angle of snout 

 profile with lengthwise axis of body 63 to 67 degrees, upper profile 

 convex. 



Shape of body nearly round in young, oval in adults; preorbital, 

 suborbital, preopercle, and subopercle serrate, opercle serrate near 

 upper edge of gill opening and with a flat triangular spine; scales on 

 snout anterior to nostrils; anterior rays of dorsal and anal longest, 

 these fins angular; caudal with two free spines near base above and 

 below, tips of lobes pointed, fin slightly forked. 



Color in alcohol. — Head and body with thi-ee broad transverse black 

 bands, the first from origin of dorsal through eye to chin, covering 

 anterior part of head, except for yellowish interorbital area, lips 

 blackish; the second from about middle of spinous dorsal through base 

 of pectoral to pelvics; the thii'd from anterior soft dorsal rays to anal 

 rays; interspaces whitish, scales with white centers, brown margins, 

 or entirely brown; anus black; spiny dorsal membranes black; tips of 

 soft dorsal rays white, posterior rays of soft anal with white tips; 

 caudal peduncle and caudal fin pale; pectoral rays pale, pelvics black. 



Color when alive. — As described for preserved specimens, except that 

 interorbital area and lips are grayish, spaces between first and second 

 black bars silvery, base of caudal dusky. 



