202 ACANTHOPTERTGII. 



Family, XV— ACANTHUKID^E, (pt.) Richards. 



Acanthurinat, pt. Swains. : Acanthuroidei, Bleeker : Acronuridoz, Giinther. 



Branchiostegals from four to seven : pseudobranchiss. Body oblong or elevated and compressed. Eyes 

 of moderate size and lateral. Cleft of mouth very slight. Teeth in both jaws in a single compressed row, 

 often lobate or serrated, and tapering incisors may be present. Palate edentulous. A single dorsal fln with 

 fewer spines than rays : anal with two or three spines : ventrals thoracic. Scales minute. Lateral line 

 complete and continuous. The side of the free portion of the tail usually armed with one or more bony 

 plates or spines, these are small or absent in the immature, developing with age. Air-vessel present, 

 forked posteriorly. Pyloric appendages few. 



SYNOPSIS OF GENERA. 



1. Acanthurus. An erectile spine on either side of the free portion of the tail : ventral usually with 

 one spine and five rays. Scales small or even rudimentary. Red Sea, East coast of Africa, through the seas of 

 India, and the tropics. 



2. Naseus. One to three non-erectile spines on either side of the free portion of the tail : ventral with 

 one spine and three rays. Scales minute or rudimentary. From the East coast of Africa through the seas of 

 India to Polynesia. 



Genus, 1 — Acanthurus,* (Forsh.) Bl. 



Opisotomus, Comm. : Harpurus, Forster : Acronurus, Cnv. (young): Keris,f pt., Cuv. (? young): 

 Ctenodon and Zabrasoma, Swains. : Scopas, Kner : Rhombotides, Bleeker. 



Branchiostegals five : pseudobranchice ivell developed. Body and head elevated and strongly compressed. 

 Eyes high up. Teeth in a single row with lobate or serrated edges. A single dorsal fin with fewer spines than rays: 

 anal with three spines : ventral usually with one spine and five rays. Scales small or minute, cycloid or ctenoid, 

 sometimes spinate. A moveable spine exists in a groove on the side of the free portion of the tail, just below the 

 lateral-line. Air-vessel large, posteriorly forked. Pyloric appendages few (5-7). 



The candal fin generally becomes more lobed or emarginate in the adults than it is in the young. In 

 some instances (see A hepatus, p. 206) the rays in the ventral fin are decreased in number and rather altered in 

 character. 



The young of this genus have no scales, but the skin is vertically striated, sometimes with small rough 

 points. In a specimen {Acanthurus melanurus, Cuv. and Val.) from Malabar, \\ inches in length, the most 

 distinct appearance of scales is to be seen along the bases of the dorsal and anal fins. There are two parallel 

 raised serrated ridges from the snout to opposite the nostril, whilst the anterior edge of the second spine of the 

 dorsal fin is serrated. In a second specimen, although slightly smaller, little sharp points or rudimentary 

 scales are to be seen, or appearing as if each ridge of the skin were ctenoid in places. In a specimen 2£ inches 

 in length, the serrations adverted to have disappeared and rudimentary scales are visible all over the body. 



SYNOPSIS OF SPECIES. 

 A. Broad teeth fixed in the jaws : 8 or 9 dorsal spines : 5 ventral rays. (Rhombotides.) 



1. Acantkiwus lineatus. D. xl-fri A. -fir- Upper two-thirds of body canary yellow, which, as well as 

 the head, have 9 or 10 oblique blue bands. A semilunar blue band in the centre of the caudal. Seas of India 

 to the Malay Archipelago. 



2. Acanthivrus leucostemon. ~D. -^toi A. j^^-g-. Blue, head dark brown, chest white as is also a ring 

 round the lower part of the mouth. A black band along base and either side of caudal fin, a second in its last 

 fourth. East coast of Africa, seas of India to the Malay Archipelago. 



3. Acanthurus aurolineatus. D. ^, A. -^. Bluish, with about 12 horizontal yellow bands, dorsal and 

 anal fins likewise banded. Coromandel coast of India. 



4. Acanthurus triostegus. D. 2-3V5, A. 2-0-2-2 • Greenish, with a black ocular band, four more down the 

 body and an interrupted one across the free portion of the tail. 



5. Acanthurus Tennentii. D. -£g, A. -£t. Brown, white hind edge to the caudal fin, and ? a dark ring on 

 the shoulder. Ceylon. 



6. Acanthurus matoides. D. ■ sr 9 -2s, A. -j-^a-g- Brown, sometimes with blue lines on the body and fins, 

 and a white ring at the base of the caudal fin. Red Sea, seas of India to the Malay Archipelago and beyond. 



* Eolili-meen, Tam. 



t The Genus Keris, C.V. appears to consist of the young of Acanthurus, or Naseus, or both. 



