ACATSTHURIDjE. 337 



in a single row with lobate or serrated edges; anal with three 

 spines ; ventral usually with one spine and live rays. Scales small 

 or minute, cycloid or ctenoid, sometimes spiny. A movable spine 

 in a groove on side of free portion of tail, just below the lateral 

 line. Air-vessel large. Pyloric appendages few (5-7). 



The caudal fin generally becomes more lobed or emarginate in 

 adults than it is in the young. In some instances (see A. hepatus, 

 p. 143) the rays in the ventral fin are diminished in number and 

 rat'.ier 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 of 

 Acanthurus melanurus from Malabar, 1^ inches in length, the 

 most distinct appearance of sciles 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 rudi- 

 mentary scales are to be seen, 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. 



Geographical Distribution. All tropical seas except the Eastern 

 Pacific. 



Synopsis of Indian Species. 



A. Broad teeth fixed in jaws ; 8 or 9 dor- 

 sal spines. 

 a. Ventral rays 5. 



Head and upper f of body canary- 

 yellow with oblique blue bands. ... 1. A. lineatus, p. 138. 



Blue, head dark brown, chest white. . 2. A. leucosternum, p. 138. 



Bluish, with about 12 longitudinal 



yellow bands 3. A. aurolineatus, p. 139. 



Greenish, with vertical black bands . . 4. A. triosteyus, p. 139. 



Brown, caudal fin white-edged 5. A. tennentii, p. 140. 



Brown, dorsal and anal banded, a 



white ring at base of caudal 0. A. matoides, p. 141. 



Blackish brown ; fins black. L. 1. 



about 150 7. A. gahm, p. 141. 



Brown, fins blackish brown. L. 1. 



about 80 8. A. celebicus, p. 142. 



Brown, a black band over occiput, 

 another over free portion of tail. 



Silvery band from opercle to chest. 9. A. melanwus, p. 142. 

 b. Ventral rays 2 10. A. hepatus, p. 143. 



B. Setiforni movable teeth dilated at their 



extremities ; 8 or 9 dorsal spines. 



V. 1/5 11. A. striyosiis, p. 143. 



C. Broad teeth fixed in jaws; 1 to 4 dor- 



sal spines. V. 1/5. 



D. 5/24-25. Blackish, caudal yellow. 12. A. xanthurus, p. 1J4. 

 D. 3-4/28-29. Brown with narrow 



blue lines 13. A. velifer, p. 144. 



