350 ACE0NtrRID.12. 



according to age, the horn being horizontal, with its axis passing 

 through the centre of the eye. The horn, in young specimens, soon 

 reaches beyond the snout, which is verj^ short ; the anterior profile of 

 the snout is subvertical, and its Icngthy^taken from the base of the 

 horn, is about equal to the diameter of the orbit. Teeth exceedingly- 

 small, finely serrated. The height of the body is one-third, or rather 

 more than one-third of the total length (the caudal fin included). 

 The length of the fifth dorsal spine equals its distance from the 

 origin of the fin. Greyish-brown, with numerous short blue trans- 

 verse lines posteriorly ; caudal light -coloured on its posterior half, 

 its margin being green. 



From Mamitius to Pol}Ticsia. 



This species has not yet been found in the Ilcd Sea. The speci- 

 mens determined by Dr. lliippell as N. hrevirostris (N. W. Fische, 

 p. 130) are immature specimens of N. fronticornis (as he himself 

 supjjoses), but entirely different from the present si)ecies. 



a. Stuffed : thirteen inches long ; horn fifteen lines, Ceylon. From 

 Dr. Sibbald's Collection. 



h. Eleven inches long ; horn one inch. Malayan Archipelago. Pre- 

 sented by Sir J. Richardsen. 



c. Eight inches long ; horn four lines. Macassar. 



d. Eight inches long ; horn three lines. Amboj-na. Purchased of 



Mr. Frank. 



e. Seven inches and a half long ; hom three lines : stuffed. Port 



llcsolution (Tana). From Mr. Macgillivray's Collection. 

 /. Six inches and a half long ; horn one line. Aneiteum. From 



Mr. Macgillivray's Collection. 

 f/. Adult : skeleton. From the Haslar Collection. 



The skeleUni has a great similarity to that of Acanthurus. The 

 form of the skull would be nearly the same but for the horn -like 

 protuberance on the forehead. The crown of the head is short and 

 convex, and there is a short triangular crest on the anterior portion 

 of the supraoccipital. The hinder side of the occiput has a vertical 

 groove above the foramen occipitale and a pair of short protuber- 

 ances, which are present also in Acanthurus. The principal frontals 

 are convex, smooth, porous, not much narrower between the orbits 

 than behind them. The prefrontals arc not prominent, forming the 

 front margin of the orbit. The borders of the principal frontals and 

 of the pra)frontals being very distinct, I conclude tliat the horn is 

 formed only by the turbinal bones, which, as we have seen above, 

 arc well developed also in Acanthurus. The same bones form the 

 rostral process in Malthe (see p. 202). The bones of the jaws are 

 as short as in Acnnihurus, but less strong and thick, the teeth being 

 much smaller than in tliat genus ; thu maxillary and intermaxillary 

 are firmly and immovcably joined together, and the latter has its 

 posterior processes extremely short. The lower jaw is elevated, 

 rather thin. Palatines short ; the bones of the tympanic cavity 

 well ossified ; the epitympanic especially is well developed, and oc- 



