1. ACANTHURUS. 331 



specimens, convex in adult ones. Brown : generally with a whitish 

 band across the root of the caudal fin, which, if present, occupies 

 more space on the fin than on the scaly portion of the tail ; it dis- 

 appears entirely in old individuals. Dorsal and anal fins with dark- 

 blue longitudinal streaks. 



East Indian Seas. Polynesia. 



a-h, G. Half-grown and young. A.mboyna. Purchasedof Mr. Frank. 



d. Half-grown : skin. Pinang. From Dr. Cantor's Collection. 



e. Young. Feejee Islands. 



/. Adult. From the Haslar Collection. 



g, h. Adult : skins. From the Collection of the Zoological Society. 



The earlier ichthyologists have confounded this species with the 

 A. chirurgus from the Atlantic, in consequence of the close affinity 

 existing between them. This affinity is so great, that we are mxich 

 inclined to consider them as mere varieties. Yet we have not seen 

 a specimen of the Atlantic form which has the profile of the snout 

 so convex as it may be seen in old Indian fishes. Valenciennes has 

 entirely overlooked the changes in the form of the caudal fin and of 

 the snout, and of colour, to which this species is subject with age, 

 and has invented specific names for every stage of developtnent. 



Acanthurus lamarrn, Cuv. & Yal. x. p. 236, also appears to be very 

 closely allied to A. matoides, but is said to have only twenty-three 

 soft rays in the anal fin. 



5. Acanthurus nigro-fuscus. 



Chaetodon nigrofuscus, Forsk. p. 64. 



Mata, Russelly i. p. 04. pi. 82. 



? Chaetodon elongatus, Laccp. iv. p. 471. pi. 6. fig. 2. 



Acanthurus nigricans. Riipp. Atl. Fische, p. 57. 



? Acanthurus mata, Cuv. 4" Val. x. p. 202. 



? nigro-fuscus, Cuv. ^- Val. x. p. 214. 



? elongatus, Cuv. ^- Val. x. p. 20G. 



^-dv- ^-.l^a- V.1/5. Vert. 9/14. 



The height of the body is one-half the total length (the caudal 

 fin not included). The distance of the nostril from the edge of the 

 upper jaw is rather less than one-half the length of the head. 

 The upper jaw with eight or nine lobate incisors on each side. 

 Caudal spine with a process posteriorly, pointing backwards. The 

 upper profile of the snout nearly straight. Uniform blackish-brown. 



Red Sea. Ceylon. Coast of Coromandcl. Amboyna. 



a. Adult : skin. Ceylon. From Dr. Kclaart's Collection. ^ 



b, c. Half-grown and young. Amboyna. Purchased of Mr. Frank. 



0. Acanthurus bipunctatus. 



D. ^. A. -. 

 The greatest depth of the body is between the ventral and anal 



