558 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.xxv. 



15. ACANTHURUS Forskal. 



Acanthurm ForskAl, Descr. Anim., 1775, p. 59 {unicornis). 

 Jtfonoceros Schneider, Syst. Ichth., 1801, p. 186 {biaculeatus) . 

 Naso Lacepede, Hist. Nat. Poiss., Ill, 1802, p. 106 {fronticomis). 

 Nasonus Rafinesque, Anal. Nature, 1815, substitute for Naso. 

 Priodon (Cuvier) Quovand GAiMARD,Voy. Uranie, Zool., 1824, p. 377 {anrmlatus). 

 Nmeus Cuvier, Regne Animal, 2d ed., II, 1829, p. 224 {fronticornw). 

 Priodontichthys Bonaparte, Destrib. Metod. Anim. Vest., 1833, p. 34 {annulatus). 

 Keris^ Cuvier and Valenciennes, Hist. Nat. Poiss., X, 1835, p. 304 {anginosm). 

 Body oblong, compressed, covered with small roughish scales; tail 

 with two large immoval^le, bony keeled plates, these entirely wanting 

 in young examples. Head in the adult with the forehead prominent, 

 developing a very long bony horn above the eyes, the horn wanting 

 in the young; teeth small in one series, slightly compressed incisors, 

 usually with serrate edges. Ventral fins incomplete, the rays I,^ 3. 

 Dorsal with 5 or 6 spines; anal with 2 spines, the small first spine 

 wanting. Intestinal canal elongate. Herbivorous fishes of the East 

 Indian and Polynesian seas, some of them remarkable for the ))ony 

 frontal projection, and for the large ornate caudal spines. 



We separate from Acanthurns the genera called CalUcantkus^ and 

 Axinurm^ {thynnoldes). The three groups may be provisionally 

 defined as follows: 



a. Forehead with an elongate, tapering, subcylindrieal horn in the adult; tail with 



two bony plates; teeth small, serrulate AcanDmrHs. 



aa. Forehead without subcylindrieal horn; the snout with or without a compressed 

 crest. 

 t,. Tail with two bony plates; dorsal spines 5 or 6; teeth aerrnX&ie.. Callkardhxis.''^ 

 hh. Tail with one bony plate; dorsal spines 4; teeth entire A.dnurus.' 



It seems to us that the generic name Acanthurm is available for the 

 genus rather than the later name, 3fonoeeros. The genus Acanfkurxs 

 as founded ])y Forskal includes this genus and Teuthis. The first spe- 

 cies named by Forskal, unlcm^nis being taken as its type, Acimthurus 

 becomes equivalent to Monoceros. If we follow the rule of allowing 

 subsequent authors to fix the type, Acauthurvx l)ecomes, of course, a 

 synonym of Toithis, and the present genus must be called Monocerus. 



[aKavOa^ spine; ovpa^ tail.) 



•The definition of the supposed genus Keris applies to the young of Xesimis. 

 (Ventral rays I, 5; anal spines 3.) But the figure of Kens anginosus does not sup- 

 port the description, and the number of fin rays shows it to be the young of some 

 Acunthurus. 



^ Callicanlhus Swamson, Class. Fishes, II, 1839, p. 256 {elegans). 



■^Arinurus Cuvier and Valenciennes, Hist. Poiss., X, 1835, p. 225 {thi,nnoides) . 



